Use ContextProvider subclass to provide WGC3D pointers

content/renderer/render_thread_impl.h

Index: content/renderer/render_thread_impl.h
diff --git a/content/renderer/render_thread_impl.h b/content/renderer/render_thread_impl.h
index 8fb3ad9f6281a5f4d88c09c177d230ddc6ae3c93..74e054e60bbabaacdf40c7343188e17b397a6f2a 100644
--- a/content/renderer/render_thread_impl.h
+++ b/content/renderer/render_thread_impl.h
@@ -69,6 +69,7 @@ class AudioInputMessageFilter;
 class AudioMessageFilter;
 class AudioRendererMixerManager;
 class ContextProviderCommandBuffer;
+class ContextProviderWebContext;
 class DBMessageFilter;
 class DevToolsAgentFilter;
 class DomStorageDispatcher;
@@ -265,7 +266,7 @@ class CONTENT_EXPORT RenderThreadImpl : public RenderThread,
   scoped_refptr<RendererGpuVideoAcceleratorFactories> GetGpuFactories();
 
   scoped_refptr<cc::ContextProvider> OffscreenCompositorContextProvider();
-  scoped_refptr<cc::ContextProvider> SharedMainThreadContextProvider();
+  scoped_refptr<ContextProviderWebContext> SharedMainThreadContextProvider();
 
   // AudioRendererMixerManager instance which manages renderer side mixer
   // instances shared based on configured audio parameters.  Lazily created on