Adding Angular and dependent packages for testing

third_party/pkg/angular/lib/tools/io_impl.dart

+library angular.io_impl;
+
+import 'dart:io';
+import 'io.dart';
+
+class IoServiceImpl implements IoService {
+
+  String readAsStringSync(String filePath) =>
+      new File(filePath).readAsStringSync();
+
+  void visitFs(String rootDir, FsVisitor visitor) {
+    Directory root = new Directory(rootDir);
+    if (!FileSystemEntity.isDirectorySync(rootDir)) {
+      throw 'Expected $rootDir to be a directory!';
+    }
+    root.listSync(recursive: true, followLinks: true).forEach((entity) {
+      if (entity.statSync().type == FileSystemEntityType.FILE) {
+        visitor(entity.path);
+      }
+    });
+  }
+}