Stop running pub get at gclient sync time and fix build bugs

mojo/public/dart/third_party/shelf/lib/src/pipeline.dart

+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library shelf.pipeline;
+
+import 'handler.dart';
+import 'middleware.dart';
+
+/// A helper that makes it easy to compose a set of [Middleware] and a
+/// [Handler].
+///
+///     var handler = const Pipeline()
+///         .addMiddleware(loggingMiddleware)
+///         .addMiddleware(cachingMiddleware)
+///         .addHandler(application);
+class Pipeline {
+  final Pipeline _parent;
+  final Middleware _middleware;
+
+  const Pipeline()
+      : _middleware = null,
+        _parent = null;
+
+  Pipeline._(this._middleware, this._parent);
+
+  /// Returns a new [Pipeline] with [middleware] added to the existing set of
+  /// [Middleware].
+  ///
+  /// [middleware] will be the last [Middleware] to process a request and
+  /// the first to process a response.
+  Pipeline addMiddleware(Middleware middleware) =>
+      new Pipeline._(middleware, this);
+
+  /// Returns a new [Handler] with [handler] as the final processor of a
+  /// [Request] if all of the middleware in the pipeline have passed the request
+  /// through.
+  Handler addHandler(Handler handler) {
+    if (_middleware == null) return handler;
+    return _parent.addHandler(_middleware(handler));
+  }
+
+  /// Exposes this pipeline of [Middleware] as a single middleware instance.
+  Middleware get middleware => addHandler;
+}