Add compile flag for enabling the compostior

sky/viewer/document_view.h

 // Copyright 2014 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.
 
 #ifndef SKY_VIEWER_DOCUMENT_VIEW_H_
 #define SKY_VIEWER_DOCUMENT_VIEW_H_
 
 #include "base/compiler_specific.h"
 #include "base/memory/weak_ptr.h"
 #include "mojo/public/cpp/application/lazy_interface_ptr.h"
@@ skipping 48 matching lines @@
 
   mojo::Shell* shell() const { return shell_.get(); }
 
  private:
   // Application methods:
   void AcceptConnection(const mojo::String& requestor_url,
                         mojo::ServiceProviderPtr provider) override;
   void Initialize(mojo::Array<mojo::String> args) override;
 
   // WebWidgetClient methods:
-  virtual blink::WebLayerTreeView* initializeLayerTreeView();
+  blink::WebLayerTreeView* initializeLayerTreeView() override;
+  void scheduleAnimation() override;
 
   // WebFrameClient methods:
   mojo::View* createChildFrame(const blink::WebURL& url) override;
   void frameDetached(blink::WebFrame*) override;
   blink::WebNavigationPolicy decidePolicyForNavigation(
     const blink::WebFrameClient::NavigationPolicyInfo& info) override;
   void didAddMessageToConsole(
       const blink::WebConsoleMessage& message,
       const blink::WebString& source_name,
       unsigned source_line,
@@ skipping 44 matching lines @@
   scoped_ptr<ScriptRunner> script_runner_;
   int debugger_id_;
 
   base::WeakPtrFactory<DocumentView> weak_factory_;
   DISALLOW_COPY_AND_ASSIGN(DocumentView);
 };
 
 }  // namespace sky
 
 #endif  // SKY_VIEWER_DOCUMENT_VIEW_H_