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

Fixes https://github.com/flutter/flutter/issues/10630
diff --git a/packages/flutter_tools/test/android/gradle_test.dart b/packages/flutter_tools/test/android/gradle_test.dart
new file mode 100644
index 0000000..457ba81
--- /dev/null
+++ b/packages/flutter_tools/test/android/gradle_test.dart
@@ -0,0 +1,34 @@
+// 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,
+    });
+  });
+}