Adding Angular and dependent packages for testing

third_party/pkg/angular/test/tools/mock_io_service.dart

+library angular.mock_io;
+
+import 'package:angular/tools/io.dart';
+
+class MockIoService implements IoService {
+
+  Map<String, String> mockData;
+
+  MockIoService(this.mockData);
+
+  String readAsStringSync(String filePath) {
+    if (!mockData.containsKey(filePath)) {
+      throw 'file not found';
+    }
+    return mockData[filePath];
+  }
+
+  void visitFs(String rootDir, visitor(String file)) {
+    mockData.keys.forEach((file) => visitor(file));
+  }
+}