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

cc/test/fake_layer_tree_host_client.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/test/fake_layer_tree_host_client.h"
 
 #include "cc/output/context_provider.h"
 #include "cc/test/test_web_graphics_context_3d.h"
 
 namespace cc {
 
 FakeLayerTreeHostClient::FakeLayerTreeHostClient(RendererOptions options)
     : use_software_rendering_(options == DIRECT_SOFTWARE ||
                               options == DELEGATED_SOFTWARE),
       use_delegating_renderer_(options == DELEGATED_3D ||
                                options == DELEGATED_SOFTWARE) {}
 
 FakeLayerTreeHostClient::~FakeLayerTreeHostClient() {}
 
-scoped_ptr<OutputSurface> FakeLayerTreeHostClient::CreateOutputSurface() {
+scoped_ptr<OutputSurface> FakeLayerTreeHostClient::CreateOutputSurface(
+    bool fallback) {
   if (use_software_rendering_) {
     if (use_delegating_renderer_) {
       return FakeOutputSurface::CreateDelegatingSoftware(
           make_scoped_ptr(new SoftwareOutputDevice)).PassAs<OutputSurface>();
     }
 
     return FakeOutputSurface::CreateSoftware(
         make_scoped_ptr(new SoftwareOutputDevice)).PassAs<OutputSurface>();
   }
 
@@ skipping 16 matching lines @@
 
 scoped_refptr<cc::ContextProvider> FakeLayerTreeHostClient::
     OffscreenContextProviderForCompositorThread() {
   if (!compositor_thread_contexts_.get() ||
       compositor_thread_contexts_->DestroyedOnMainThread())
     compositor_thread_contexts_ = FakeContextProvider::Create();
   return compositor_thread_contexts_;
 }
 
 }  // namespace cc