Fall back to software mode if Aura can't create a GL context

ui/compositor/test/default_context_factory.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 "ui/compositor/test/default_context_factory.h"
 
 #include "cc/output/output_surface.h"
 #include "ui/compositor/reflector.h"
 #include "ui/gl/gl_implementation.h"
 #include "ui/gl/gl_surface.h"
@@ skipping 12 matching lines @@
 bool DefaultContextFactory::Initialize() {
   if (!gfx::GLSurface::InitializeOneOff() ||
       gfx::GetGLImplementation() == gfx::kGLImplementationNone) {
     LOG(ERROR) << "Could not load the GL bindings";
     return false;
   }
   return true;
 }
 
 scoped_ptr<cc::OutputSurface> DefaultContextFactory::CreateOutputSurface(
-    Compositor* compositor) {
+    Compositor* compositor, bool software_fallback) {
+  DCHECK(!software_fallback);
   blink::WebGraphicsContext3D::Attributes attrs;
   attrs.depth = false;
   attrs.stencil = false;
   attrs.antialias = false;
   attrs.shareResources = true;
 
   using webkit::gpu::WebGraphicsContext3DInProcessCommandBufferImpl;
   scoped_ptr<WebGraphicsContext3DInProcessCommandBufferImpl> context3d(
       WebGraphicsContext3DInProcessCommandBufferImpl::CreateViewContext(
           attrs, compositor->widget()));
@@ skipping 47 matching lines @@
 
   return shared_main_thread_contexts_;
 }
 
 void DefaultContextFactory::RemoveCompositor(Compositor* compositor) {
 }
 
 bool DefaultContextFactory::DoesCreateTestContexts() { return false; }
 
 }  // namespace ui