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

cc/test/layer_tree_test.h

Index: cc/test/layer_tree_test.h
diff --git a/cc/test/layer_tree_test.h b/cc/test/layer_tree_test.h
index 556378b0aeb4ed66f175cc2eac7d9c07267dc3fa..71e74d2d996048161c18de04ff0a127ec7081469 100644
--- a/cc/test/layer_tree_test.h
+++ b/cc/test/layer_tree_test.h
@@ -70,9 +70,9 @@ class TestHooks : public AnimationDelegate {
   virtual void NotifyAnimationStarted(double time) OVERRIDE {}
   virtual void NotifyAnimationFinished(double time) OVERRIDE {}
 
-  virtual scoped_ptr<OutputSurface> CreateOutputSurface() = 0;
+  virtual scoped_ptr<OutputSurface> CreateOutputSurface(bool fallback) = 0;
   virtual scoped_refptr<cc::ContextProvider>
-      OffscreenContextProviderForMainThread() = 0;
+  OffscreenContextProviderForMainThread() = 0;
   virtual scoped_refptr<cc::ContextProvider>
       OffscreenContextProviderForCompositorThread() = 0;
 };
@@ -153,9 +153,9 @@ class LayerTreeTest : public testing::Test, public TestHooks {
   bool delegating_renderer() const { return delegating_renderer_; }
   FakeOutputSurface* output_surface() { return output_surface_; }
 
-  virtual scoped_ptr<OutputSurface> CreateOutputSurface() OVERRIDE;
+  virtual scoped_ptr<OutputSurface> CreateOutputSurface(bool fallback) OVERRIDE;
   virtual scoped_refptr<cc::ContextProvider>
-      OffscreenContextProviderForMainThread() OVERRIDE;
+  OffscreenContextProviderForMainThread() OVERRIDE;
   virtual scoped_refptr<cc::ContextProvider>
       OffscreenContextProviderForCompositorThread() OVERRIDE;