switch const finder to package_config (flutter#19576)

Generate package config during gclient runhooks and update BUILD.gn to reference it

Author: jonahwilliams

tools/const_finder/.dart_tool/package_config.json

@@ -2,37 +2,34 @@
   "configVersion": 2,
   "packages": [
     {
-      "name": "args",
-      "rootUri": "../../../../third_party/dart/third_party/pkg/args",
-      "packageUri": "lib/",
-      "languageVersion": "2.0"
+      "name": "const_finder",
+      "rootUri": "../",
+      "packageUri": "lib",
+      "languageVersion": "2.4"
     },
     {
       "name": "kernel",
       "rootUri": "../../../../third_party/dart/pkg/kernel",
-      "packageUri": "lib/",
+      "packageUri": "lib",
       "languageVersion": "2.2"
     },
     {
       "name": "meta",
       "rootUri": "../../../../third_party/dart/pkg/meta",
-      "packageUri": "lib/",
-      "languageVersion": "1.12"
+      "packageUri": "lib",
+      "languageVersion": "2.9"
+    },
+    {
+      "name": "args",
+      "rootUri": "../../../../third_party/dart/third_party/pkg/args",
+      "packageUri": "lib",
+      "languageVersion": "2.3"
     },
     {
       "name": "path",
       "rootUri": "../../../../third_party/dart/third_party/pkg/path",
-      "packageUri": "lib/",
+      "packageUri": "lib",
       "languageVersion": "2.0"
-    },
-    {
-      "name": "const_finder",
-      "rootUri": "../",
-      "packageUri": "lib/",
-      "languageVersion": "2.4"
     }
-  ],
-  "generated": "2020-01-16T19:11:54.963296Z",
-  "generator": "pub",
-  "generatorVersion": "2.7.0"
-}
+  ]
+}

tools/const_finder/BUILD.gn

@@ -6,7 +6,7 @@ import("//third_party/dart/utils/application_snapshot.gni")
 
 application_snapshot("const_finder") {
   main_dart = "bin/main.dart"
-  dot_packages = ".packages"
+  dot_packages = ".dart_tool/package_config.json"
 
   training_args = [ "--help" ]
 

tools/run_third_party_dart.py

@@ -7,3 +7,4 @@
 if __name__ == '__main__':
     subprocess.call(["src/third_party/dart/tools/sdks/dart-sdk/bin/dart", "pub", "global", "activate", "-spath", "./src/flutter/tools/generate_package_config"])
     subprocess.call(["src/third_party/dart/tools/sdks/dart-sdk/bin/dart", "pub", "global", "run", "generate_package_config:generate_from_legacy", "src/flutter/flutter_frontend_server/.packages"])
+    subprocess.call(["src/third_party/dart/tools/sdks/dart-sdk/bin/dart", "pub", "global", "run", "generate_package_config:generate_from_legacy", "src/flutter/tools/const_finder/.packages"])