Look for APKs at the path used by Android Gradle plugin 3.0 (#10798)

Fixes https://github.com/flutter/flutter/issues/10630

packages/flutter_tools/lib/src/android/gradle.dart

@@ -211,6 +211,17 @@ Future<Null> buildGradleProjectV1(String gradle) async {
   printStatus('Built $gradleAppOutV1 (${getSizeAsMB(apkFile.lengthSync())}).');
 }
 
+File findApkFile(String buildDirectory, String buildModeName) {
+  final String apkFilename = 'app-$buildModeName.apk';
+  File apkFile = fs.file('$buildDirectory/$apkFilename');
+  if (apkFile.existsSync())
+    return apkFile;
+  apkFile = fs.file('$buildDirectory/$buildModeName/$apkFilename');
+  if (apkFile.existsSync())
+    return apkFile;
+  return null;
+}
+
 Future<Null> buildGradleProjectV2(String gradle, String buildModeName, String target, String kernelPath) async {
   final String assembleTask = "assemble${toTitleCase(buildModeName)}";
 
@@ -244,8 +255,9 @@ Future<Null> buildGradleProjectV2(String gradle, String buildModeName, String ta
     throwToolExit('Gradle build failed: $exitcode', exitCode: exitcode);
 
   final String buildDirectory = getGradleAppOutDirV2();
-  final String apkFilename = 'app-$buildModeName.apk';
-  final File apkFile = fs.file('$buildDirectory/$apkFilename');
+  final File apkFile = findApkFile(buildDirectory, buildModeName);
+  if (apkFile == null)
+    throwToolExit('Gradle build failed to produce an Android package.');
   // Copy the APK to app.apk, so `flutter run`, `flutter install`, etc. can find it.
   apkFile.copySync('$buildDirectory/app.apk');
 

packages/flutter_tools/test/android/gradle_test.dart

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:file/file.dart';
+import 'package:file/memory.dart';
+import 'package:flutter_tools/src/android/gradle.dart';
+import 'package:test/test.dart';
+
+import '../src/context.dart';
+
+const String _kBuildDirectory = '/build/app/outputs';
+
+void main() {
+  FileSystem fs;
+
+  setUp(() {
+    fs = new MemoryFileSystem();
+    fs.directory('$_kBuildDirectory/release').createSync(recursive: true);
+    fs.file('$_kBuildDirectory/app-debug.apk').createSync();
+    fs.file('$_kBuildDirectory/release/app-release.apk').createSync();
+  });
+
+  group('gradle', () {
+    testUsingContext('findApkFile', () {
+      expect(findApkFile(_kBuildDirectory, 'debug').path,
+             '/build/app/outputs/app-debug.apk');
+      expect(findApkFile(_kBuildDirectory, 'release').path,
+             '/build/app/outputs/release/app-release.apk');
+    }, overrides: <Type, Generator>{
+      FileSystem: () => fs,
+    });
+  });
+}