Clone goldens as part of flutter update-packages.

flutter_tools cannot depend on flutter_goldens (as flutter_goldens
depdends on the Flutter sdk), so this commit splits client.dart from
flutter_goldens to a pure-dart flutter_goldens_client package.

packages/flutter_goldens/lib/flutter_goldens.dart

@@ -11,8 +11,8 @@ import 'package:file/local.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:meta/meta.dart';
 
-import 'client.dart';
-export 'client.dart';
+import 'package:flutter_goldens_client/client.dart';
+export 'package:flutter_goldens_client/client.dart';
 
 /// Main method that can be used in a `flutter_test_config.dart` file to set
 /// [goldenFileComparator] to an instance of [FlutterGoldenFileComparator] that

packages/flutter_goldens/pubspec.yaml

@@ -13,6 +13,8 @@ dependencies:
   meta: 1.1.6
   platform: 2.2.0
   process: 3.0.5
+  flutter_goldens_client:
+    path: ../flutter_goldens_client
 
   analyzer: 0.32.4 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   args: 1.5.0 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"

packages/flutter_goldens_client/analysis_options.yaml

+# Use the analysis options settings from the top level of the repo (not
+# the ones from above, which include the `public_member_api_docs` rule).
+
+include: ../../analysis_options.yaml

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

@@ -6,6 +6,7 @@ import 'dart:async';
 import 'dart:collection';
 
 import 'package:meta/meta.dart';
+import 'package:flutter_goldens_client/client.dart';
 
 import '../base/common.dart';
 import '../base/file_system.dart';
@@ -107,6 +108,13 @@ class UpdatePackagesCommand extends FlutterCommand {
     final bool isPrintTransitiveClosure = argResults['transitive-closure'];
     final bool isVerifyOnly = argResults['verify-only'];
 
+    // The dev/integration_tests/android_views integration test depends on an assets
+    // package that is in the goldens repository. We need to make sure that the goldens
+    // repository is cloned locally before we verify or update pubspecs.
+    printStatus('Cloning goldens repository...');
+    final GoldensClient goldensClient = new GoldensClient();
+    await goldensClient.prepare();
+
     if (isVerifyOnly) {
       bool needsUpdate = false;
       printStatus('Verifying pubspecs...');

packages/flutter_tools/pubspec.yaml

@@ -36,6 +36,8 @@ dependencies:
   web_socket_channel: 1.0.9
   xml: 3.0.1
   yaml: 2.1.15
+  flutter_goldens_client:
+    path: ../flutter_goldens_client
 
   # We depend on very specific internal implementation details of the
   # 'test' package, which change between versions, so when upgrading