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 6e77c996c5f0f9435164db1c1d0b1914881a980d..da0b1a09c1f9b4e7c0c1f5c2f67176f0c32c6189 100644
--- a/content/renderer/render_thread_impl.h
+++ b/content/renderer/render_thread_impl.h
@@ -58,6 +58,7 @@ class Extension;
 
 namespace webkit {
 namespace gpu {
+class ContextProviderWebContext;
 class GrContextForWebGraphicsContext3D;
 }
 }
@@ -262,7 +263,8 @@ class CONTENT_EXPORT RenderThreadImpl : public RenderThread,
   scoped_refptr<RendererGpuVideoAcceleratorFactories> GetGpuFactories();
 
   scoped_refptr<cc::ContextProvider> OffscreenCompositorContextProvider();
-  scoped_refptr<cc::ContextProvider> SharedMainThreadContextProvider();
+  scoped_refptr<webkit::gpu::ContextProviderWebContext>
+      SharedMainThreadContextProvider();
 
   // AudioRendererMixerManager instance which manages renderer side mixer
   // instances shared based on configured audio parameters.  Lazily created on