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

cc/test/layer_tree_pixel_test.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.
 
 #include <vector>
 
 #include "base/files/file_path.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "cc/test/layer_tree_test.h"
@@ skipping 10 matching lines @@
 class PixelComparator;
 class SolidColorLayer;
 class TextureLayer;
 class TextureMailbox;
 
 class LayerTreePixelTest : public LayerTreeTest {
  protected:
   LayerTreePixelTest();
   virtual ~LayerTreePixelTest();
 
-  virtual scoped_ptr<OutputSurface> CreateOutputSurface() OVERRIDE;
+  virtual scoped_ptr<OutputSurface> CreateOutputSurface(bool fallback) OVERRIDE;
   virtual scoped_refptr<cc::ContextProvider>
       OffscreenContextProviderForMainThread() OVERRIDE;
   virtual scoped_refptr<cc::ContextProvider>
       OffscreenContextProviderForCompositorThread() OVERRIDE;
 
   virtual scoped_ptr<CopyOutputRequest> CreateCopyOutputRequest();
 
   void ReadbackResult(scoped_ptr<CopyOutputResult> result);
 
   virtual void BeginTest() OVERRIDE;
@@ skipping 54 matching lines @@
   Layer* readback_target_;
   base::FilePath ref_file_;
   scoped_ptr<SkBitmap> result_bitmap_;
   std::vector<scoped_refptr<TextureLayer> > texture_layers_;
   int pending_texture_mailbox_callbacks_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TEST_LAYER_TREE_PIXEL_TEST_H_