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

cc/trees/layer_tree_host_unittest_context.cc

 // Copyright 2012 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/trees/layer_tree_host.h"
 
 #include "base/basictypes.h"
 #include "cc/layers/content_layer.h"
 #include "cc/layers/heads_up_display_layer.h"
 #include "cc/layers/io_surface_layer.h"
@@ skipping 1557 matching lines @@
 
 // Not reusing LayerTreeTest because it expects creating LTH to always succeed.
 class LayerTreeHostTestCannotCreateIfCannotCreateOutputSurface
     : public testing::Test,
       public FakeLayerTreeHostClient {
  public:
   LayerTreeHostTestCannotCreateIfCannotCreateOutputSurface()
       : FakeLayerTreeHostClient(FakeLayerTreeHostClient::DIRECT_3D) {}
 
   // FakeLayerTreeHostClient implementation.
-  virtual scoped_ptr<OutputSurface> CreateOutputSurface() OVERRIDE {
+  virtual scoped_ptr<OutputSurface> CreateOutputSurface(bool fallback)
+      OVERRIDE {
     return scoped_ptr<OutputSurface>();
   }
 
   void RunTest(bool threaded,
                bool delegating_renderer,
                bool impl_side_painting) {
     scoped_ptr<base::Thread> impl_thread;
     if (threaded) {
       impl_thread.reset(new base::Thread("LayerTreeTest"));
       ASSERT_TRUE(impl_thread->Start());
       ASSERT_TRUE(impl_thread->message_loop_proxy().get());
     }
 
     LayerTreeSettings settings;
     settings.impl_side_painting = impl_side_painting;
     scoped_ptr<LayerTreeHost> layer_tree_host = LayerTreeHost::Create(
         this,
         settings,
         impl_thread ? impl_thread->message_loop_proxy() : NULL);
     EXPECT_FALSE(layer_tree_host);
   }
 };
 
 SINGLE_AND_MULTI_THREAD_TEST_F(
     LayerTreeHostTestCannotCreateIfCannotCreateOutputSurface);
 
 }  // namespace
 }  // namespace cc