[webview_flutter] Move native implementations to their own packages in preparation for federated architecture

packages/webview_flutter/webview_flutter/analysis_options.yaml

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+include: ../../../analysis_options_legacy.yaml

packages/webview_flutter/webview_flutter_android/CHANGELOG.md

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+## 0.0.1
+
+* Initial release.

packages/webview_flutter/webview_flutter_android/LICENSE

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+Copyright 2013 The Flutter Authors. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without modification,
+are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google Inc. nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

packages/webview_flutter/webview_flutter_android/README.md

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+# webview\_flutter\_android
+
+The Android implementation of [`webview_flutter`][1].
+
+## Usage
+
+This package is [endorsed][2], which means you can simply use `webview_flutter`
+normally. This package will be automatically included in your app when you do.
+
+[1]: https://pub.dev/packages/webview_flutter
+[2]: https://flutter.dev/docs/development/packages-and-plugins/developing-packages#endorsed-federated-plugin

packages/webview_flutter/webview_flutter_android/analysis_options.yaml

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+include: ../../../analysis_options_legacy.yaml

packages/webview_flutter/webview_flutter_android/android/build.gradle

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+group 'io.flutter.plugins.webviewflutter'
+version '1.0-SNAPSHOT'
+
+buildscript {
+    repositories {
+        google()
+        mavenCentral()
+    }
+
+    dependencies {
+        classpath 'com.android.tools.build:gradle:3.3.0'
+    }
+}
+
+rootProject.allprojects {
+    repositories {
+        google()
+        mavenCentral()
+    }
+}
+
+apply plugin: 'com.android.library'
+
+android {
+    compileSdkVersion 29
+
+    defaultConfig {
+        minSdkVersion 19
+        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
+    }
+
+    lintOptions {
+        disable 'InvalidPackage'
+        disable 'GradleDependency'
+    }
+
+    dependencies {
+        implementation 'androidx.annotation:annotation:1.0.0'
+        implementation 'androidx.webkit:webkit:1.0.0'
+        testImplementation 'junit:junit:4.12'
+        testImplementation 'org.mockito:mockito-inline:3.11.1'
+        testImplementation 'androidx.test:core:1.3.0'
+    }
+
+
+    testOptions {
+        unitTests.includeAndroidResources = true
+        unitTests.returnDefaultValues = true
+        unitTests.all {
+            testLogging {
+               events "passed", "skipped", "failed", "standardOut", "standardError"
+               outputs.upToDateWhen {false}
+               showStandardStreams = true
+            }
+        }
+    }
+}

packages/webview_flutter/webview_flutter_android/android/settings.gradle

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+rootProject.name = 'webview_flutter'

packages/webview_flutter/webview_flutter_android/android/src/main/AndroidManifest.xml

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+<manifest package="io.flutter.plugins.webviewflutter">
+</manifest>

packages/webview_flutter/webview_flutter_android/android/src/main/java/io/flutter/plugins/webviewflutter/DisplayListenerProxy.java

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+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package io.flutter.plugins.webviewflutter;
+
+import static android.hardware.display.DisplayManager.DisplayListener;
+
+import android.annotation.TargetApi;
+import android.hardware.display.DisplayManager;
+import android.os.Build;
+import android.util.Log;
+import java.lang.reflect.Field;
+import java.util.ArrayList;
+
+/**
+ * Works around an Android WebView bug by filtering some DisplayListener invocations.
+ *
+ * <p>Older Android WebView versions had assumed that when {@link DisplayListener#onDisplayChanged}
+ * is invoked, the display ID it is provided is of a valid display. However it turns out that when a
+ * display is removed Android may call onDisplayChanged with the ID of the removed display, in this
+ * case the Android WebView code tries to fetch and use the display with this ID and crashes with an
+ * NPE.
+ *
+ * <p>This issue was fixed in the Android WebView code in
+ * https://chromium-review.googlesource.com/517913 which is available starting WebView version
+ * 58.0.3029.125 however older webviews in the wild still have this issue.
+ *
+ * <p>Since Flutter removes virtual displays whenever a platform view is resized the webview crash
+ * is more likely to happen than other apps. And users were reporting this issue see:
+ * https://github.com/flutter/flutter/issues/30420
+ *
+ * <p>This class works around the webview bug by unregistering the WebView's DisplayListener, and
+ * instead registering its own DisplayListener which delegates the callbacks to the WebView's
+ * listener unless it's a onDisplayChanged for an invalid display.
+ *
+ * <p>I did not find a clean way to get a handle of the WebView's DisplayListener so I'm using
+ * reflection to fetch all registered listeners before and after initializing a webview. In the
+ * first initialization of a webview within the process the difference between the lists is the
+ * webview's display listener.
+ */
+@TargetApi(Build.VERSION_CODES.KITKAT)
+class DisplayListenerProxy {
+  private static final String TAG = "DisplayListenerProxy";
+
+  private ArrayList<DisplayListener> listenersBeforeWebView;
+
+  /** Should be called prior to the webview's initialization. */
+  void onPreWebViewInitialization(DisplayManager displayManager) {
+    listenersBeforeWebView = yoinkDisplayListeners(displayManager);
+  }
+
+  /** Should be called after the webview's initialization. */
+  void onPostWebViewInitialization(final DisplayManager displayManager) {
+    final ArrayList<DisplayListener> webViewListeners = yoinkDisplayListeners(displayManager);
+    // We recorded the list of listeners prior to initializing webview, any new listeners we see
+    // after initializing the webview are listeners added by the webview.
+    webViewListeners.removeAll(listenersBeforeWebView);
+
+    if (webViewListeners.isEmpty()) {
+      // The Android WebView registers a single display listener per process (even if there
+      // are multiple WebView instances) so this list is expected to be non-empty only the
+      // first time a webview is initialized.
+      // Note that in an add2app scenario if the application had instantiated a non Flutter
+      // WebView prior to instantiating the Flutter WebView we are not able to get a reference
+      // to the WebView's display listener and can't work around the bug.
+      //
+      // This means that webview resizes in add2app Flutter apps with a non Flutter WebView
+      // running on a system with a webview prior to 58.0.3029.125 may crash (the Android's
+      // behavior seems to be racy so it doesn't always happen).
+      return;
+    }
+
+    for (DisplayListener webViewListener : webViewListeners) {
+      // Note that while DisplayManager.unregisterDisplayListener throws when given an
+      // unregistered listener, this isn't an issue as the WebView code never calls
+      // unregisterDisplayListener.
+      displayManager.unregisterDisplayListener(webViewListener);
+
+      // We never explicitly unregister this listener as the webview's listener is never
+      // unregistered (it's released when the process is terminated).
+      displayManager.registerDisplayListener(
+          new DisplayListener() {
+            @Override
+            public void onDisplayAdded(int displayId) {
+              for (DisplayListener webViewListener : webViewListeners) {
+                webViewListener.onDisplayAdded(displayId);
+              }
+            }
+
+            @Override
+            public void onDisplayRemoved(int displayId) {
+              for (DisplayListener webViewListener : webViewListeners) {
+                webViewListener.onDisplayRemoved(displayId);
+              }
+            }
+
+            @Override
+            public void onDisplayChanged(int displayId) {
+              if (displayManager.getDisplay(displayId) == null) {
+                return;
+              }
+              for (DisplayListener webViewListener : webViewListeners) {
+                webViewListener.onDisplayChanged(displayId);
+              }
+            }
+          },
+          null);
+    }
+  }
+
+  @SuppressWarnings({"unchecked", "PrivateApi"})
+  private static ArrayList<DisplayListener> yoinkDisplayListeners(DisplayManager displayManager) {
+    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.P) {
+      // We cannot use reflection on Android P, but it shouldn't matter as it shipped
+      // with WebView 66.0.3359.158 and the WebView version the bug this code is working around was
+      // fixed in 61.0.3116.0.
+      return new ArrayList<>();
+    }
+    try {
+      Field displayManagerGlobalField = DisplayManager.class.getDeclaredField("mGlobal");
+      displayManagerGlobalField.setAccessible(true);
+      Object displayManagerGlobal = displayManagerGlobalField.get(displayManager);
+      Field displayListenersField =
+          displayManagerGlobal.getClass().getDeclaredField("mDisplayListeners");
+      displayListenersField.setAccessible(true);
+      ArrayList<Object> delegates =
+          (ArrayList<Object>) displayListenersField.get(displayManagerGlobal);
+
+      Field listenerField = null;
+      ArrayList<DisplayManager.DisplayListener> listeners = new ArrayList<>();
+      for (Object delegate : delegates) {
+        if (listenerField == null) {
+          listenerField = delegate.getClass().getField("mListener");
+          listenerField.setAccessible(true);
+        }
+        DisplayManager.DisplayListener listener =
+            (DisplayManager.DisplayListener) listenerField.get(delegate);
+        listeners.add(listener);
+      }
+      return listeners;
+    } catch (NoSuchFieldException | IllegalAccessException e) {
+      Log.w(TAG, "Could not extract WebView's display listeners. " + e);
+      return new ArrayList<>();
+    }
+  }
+}