Support ARM 32 and 64 bits in app bundles

dev/devicelab/bin/tasks/gradle_plugin_test.dart

@@ -63,6 +63,51 @@ Future<void> main() async {
       await runProjectTest((FlutterProject project) async {
         section('gradlew assembleRelease');
         await project.runGradleTask('assembleRelease');
+
+        // When the platform-target isn't specified, we generate the snapshots
+        // for arm and arm64.
+        final List<String> targetPlatforms = <String>[
+          'android-arm',
+          'android-arm64'
+        ];
+        for (final String targetPlatform in targetPlatforms) {
+          final String androidArmSnapshotPath = path.join(
+              project.rootPath,
+              'build',
+              'app',
+              'intermediates',
+              'flutter',
+              'release',
+              targetPlatform);
+
+          final String isolateSnapshotData =
+              path.join(androidArmSnapshotPath, 'isolate_snapshot_data');
+          if (!File(isolateSnapshotData).existsSync()) {
+            throw TaskResult.failure(
+                'Snapshot doesn\'t exist: $isolateSnapshotData');
+          }
+
+          final String isolateSnapshotInstr =
+              path.join(androidArmSnapshotPath, 'isolate_snapshot_instr');
+          if (!File(isolateSnapshotInstr).existsSync()) {
+            throw TaskResult.failure(
+                'Snapshot doesn\'t exist: $isolateSnapshotInstr');
+          }
+
+          final String vmSnapshotData =
+              path.join(androidArmSnapshotPath, 'vm_snapshot_data');
+          if (!File(isolateSnapshotData).existsSync()) {
+            throw TaskResult.failure(
+                'Snapshot doesn\'t exist: $vmSnapshotData');
+          }
+
+          final String vmSnapshotInstr =
+              path.join(androidArmSnapshotPath, 'vm_snapshot_instr');
+          if (!File(isolateSnapshotData).existsSync()) {
+            throw TaskResult.failure(
+                'Snapshot doesn\'t exist: $vmSnapshotInstr');
+          }
+        }
       });
 
       await runProjectTest((FlutterProject project) async {
@@ -311,7 +356,7 @@ class _Dependencies {
 String _validateSnapshotDependency(FlutterProject project, String expectedTarget) {
   final _Dependencies deps = _Dependencies(
       path.join(project.rootPath, 'build', 'app', 'intermediates',
-          'flutter', 'debug', 'snapshot_blob.bin.d'));
+          'flutter', 'debug', 'android-arm', 'snapshot_blob.bin.d'));
   return deps.target == expectedTarget ? null :
     'Dependency file should have $expectedTarget as target. Instead has ${deps.target}';
 }

packages/flutter_tools/lib/src/commands/build_apk.dart

@@ -27,7 +27,9 @@ class BuildApkCommand extends BuildSubCommand {
       )
       ..addOption('target-platform',
         defaultsTo: 'android-arm',
-        allowed: <String>['android-arm', 'android-arm64', 'android-x86', 'android-x64']);
+        allowed: <String>['android-arm', 'android-arm64', 'android-x86', 'android-x64'],
+        help: 'The target platform for which the app is compiled.',
+      );
   }
 
   @override

packages/flutter_tools/lib/src/commands/build_appbundle.dart

@@ -20,23 +20,30 @@ class BuildAppBundleCommand extends BuildSubCommand {
 
     argParser
       ..addFlag('track-widget-creation', negatable: false, hide: !verboseHelp)
-      ..addFlag('build-shared-library',
+      ..addFlag(
+        'build-shared-library',
         negatable: false,
         help: 'Whether to prefer compiling to a *.so file (android only).',
       )
-      ..addOption('target-platform',
-        defaultsTo: 'android-arm',
-        allowed: <String>['android-arm', 'android-arm64']);
+      ..addOption(
+        'target-platform',
+        allowed: <String>['android-arm', 'android-arm64'],
+        help: 'The target platform for which the app is compiled.\n'
+            'By default, the bundle will include \'arm\' and \'arm64\', '
+            'which is the recommended configuration for app bundles.\n'
+            'For more, see https://developer.android.com/distribute/best-practices/develop/64-bit',
+      );
   }
 
   @override
   final String name = 'appbundle';
 
   @override
-  final String description = 'Build an Android App Bundle file from your app.\n\n'
-    'This command can build debug and release versions of an app bundle for your application. \'debug\' builds support '
-    'debugging and a quick development cycle. \'release\' builds don\'t support debugging and are '
-    'suitable for deploying to app stores. \n app bundle improves your app size';
+  final String description =
+      'Build an Android App Bundle file from your app.\n\n'
+      'This command can build debug and release versions of an app bundle for your application. \'debug\' builds support '
+      'debugging and a quick development cycle. \'release\' builds don\'t support debugging and are '
+      'suitable for deploying to app stores. \n app bundle improves your app size';
 
   @override
   Future<FlutterCommandResult> runCommand() async {