fix lint problems

Author: Kaushik Iska

shell/platform/android/io/flutter/embedding/android/MotionEventTracker.java

@@ -1,9 +1,9 @@
 package io.flutter.embedding.android;
 
+import android.util.LongSparseArray;
 import android.view.MotionEvent;
 import androidx.annotation.Nullable;
-import java.util.HashMap;
-import java.util.Map;
+import java.util.PriorityQueue;
 import java.util.concurrent.atomic.AtomicLong;
 
 /** Tracks the motion events received by the FlutterView. */
@@ -31,7 +31,8 @@ public long getId() {
     }
   }
 
-  private final Map<Long, MotionEvent> eventById;
+  private final LongSparseArray<MotionEvent> eventById;
+  private final PriorityQueue<Long> unusedEvents;
   private static MotionEventTracker INSTANCE;
 
   public static MotionEventTracker getInstance() {
@@ -42,13 +43,15 @@ public static MotionEventTracker getInstance() {
   }
 
   private MotionEventTracker() {
-    eventById = new HashMap<>();
+    eventById = new LongSparseArray<>();
+    unusedEvents = new PriorityQueue<>();
   }
 
   /** Tracks the event and returns a unique MotionEventId identifying the event. */
   public MotionEventId track(MotionEvent event) {
     MotionEventId eventId = MotionEventId.createUnique();
     eventById.put(eventId.id, event);
+    unusedEvents.add(eventId.id);
     return eventId;
   }
 
@@ -59,7 +62,18 @@ public MotionEventId track(MotionEvent event) {
    */
   @Nullable
   public MotionEvent pop(MotionEventId eventId) {
-    // TODO(kaushikiska) do the actual timestamp based book-keeping.
-    return eventById.remove(eventId.id);
+    // remove all the older events.
+    while (!unusedEvents.isEmpty() && unusedEvents.peek() < eventId.id) {
+      eventById.remove(unusedEvents.poll());
+    }
+
+    // remove the current event from the heap if it exists.
+    if (!unusedEvents.isEmpty() && unusedEvents.peek() == eventId.id) {
+      unusedEvents.poll();
+    }
+
+    MotionEvent event = eventById.get(eventId.id);
+    eventById.remove(eventId.id);
+    return event;
   }
 }