Add a flag to allow renderer to use software compositor when GL compositor doesn't work.

webkit/support/web_layer_tree_view_impl_for_testing.h

 // Copyright 2013 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 WEBKIT_SUPPORT_WEB_LAYER_TREE_VIEW_IMPL_FOR_TESTING_H_
 #define WEBKIT_SUPPORT_WEB_LAYER_TREE_VIEW_IMPL_FOR_TESTING_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "cc/trees/layer_tree_host_client.h"
 #include "third_party/WebKit/public/platform/WebLayerTreeView.h"
@@ skipping 45 matching lines @@
   virtual void renderingStats(
       WebKit::WebRenderingStats& stats) const;  // NOLINT(runtime/references)
 
   // cc::LayerTreeHostClient implementation.
   virtual void WillBeginFrame() OVERRIDE {}
   virtual void DidBeginFrame() OVERRIDE {}
   virtual void Animate(double frame_begin_time) OVERRIDE {}
   virtual void Layout() OVERRIDE;
   virtual void ApplyScrollAndScale(gfx::Vector2d scroll_delta, float page_scale)
       OVERRIDE;
-  virtual scoped_ptr<cc::OutputSurface> CreateOutputSurface() OVERRIDE;
+  virtual scoped_ptr<cc::OutputSurface> CreateOutputSurface(bool fallback)
+      OVERRIDE;
   virtual void DidInitializeOutputSurface(bool success) OVERRIDE {}
   virtual void WillCommit() OVERRIDE {}
   virtual void DidCommit() OVERRIDE {}
   virtual void DidCommitAndDrawFrame() OVERRIDE {}
   virtual void DidCompleteSwapBuffers() OVERRIDE {}
   virtual void ScheduleComposite() OVERRIDE;
   virtual scoped_refptr<cc::ContextProvider>
       OffscreenContextProviderForMainThread() OVERRIDE;
   virtual scoped_refptr<cc::ContextProvider>
       OffscreenContextProviderForCompositorThread() OVERRIDE;
 
  private:
   scoped_ptr<cc::LayerTreeHost> layer_tree_host_;
 
   DISALLOW_COPY_AND_ASSIGN(WebLayerTreeViewImplForTesting);
 };
 
 }  // namespace webkit
 
 #endif  // WEBKIT_SUPPORT_WEB_LAYER_TREE_VIEW_IMPL_FOR_TESTING_H_