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

cc/output/delegating_renderer_unittest.cc

 // 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 "cc/output/delegating_renderer.h"
 
 #include "cc/test/fake_output_surface.h"
 #include "cc/test/layer_tree_test.h"
 #include "cc/test/render_pass_test_common.h"
 #include "cc/test/render_pass_test_utils.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace cc {
 
 class DelegatingRendererTest : public LayerTreeTest {
  public:
   DelegatingRendererTest() : LayerTreeTest(), output_surface_(NULL) {}
   virtual ~DelegatingRendererTest() {}
 
-  virtual scoped_ptr<OutputSurface> CreateOutputSurface() OVERRIDE {
+  virtual scoped_ptr<OutputSurface> CreateOutputSurface(bool fallback)
+      OVERRIDE {
     scoped_ptr<FakeOutputSurface> output_surface =
         FakeOutputSurface::CreateDelegating3d();
     output_surface_ = output_surface.get();
     return output_surface.PassAs<OutputSurface>();
   }
 
  protected:
   TestWebGraphicsContext3D* context3d_;
   FakeOutputSurface* output_surface_;
 };
@@ skipping 104 matching lines @@
         21u, last_frame.delegated_frame_data->resource_list.size());
 
     EndTest();
   }
 };
 
 SINGLE_AND_MULTI_THREAD_DELEGATING_RENDERER_TEST_F(
     DelegatingRendererTestResources);
 
 }  // namespace cc