cc: Route offscreen context creation for compositor to the browser.

cc/resource_provider.cc

Index: cc/resource_provider.cc
diff --git a/cc/resource_provider.cc b/cc/resource_provider.cc
index 0ac1e181d790758f93b2debbead555e19a7a8e24..00cebf6ab1bd9d1119bf527cf4e190c31da75d15 100644
--- a/cc/resource_provider.cc
+++ b/cc/resource_provider.cc
@@ -21,6 +21,7 @@
 #include "third_party/khronos/GLES2/gl2ext.h"
 #include "ui/gfx/rect.h"
 #include "ui/gfx/vector2d.h"
+#include "ui/gl/context_provider.h"
 
 using WebKit::WebGraphicsContext3D;
 
@@ -1124,4 +1125,10 @@ void ResourceProvider::enableReadLockFences(ResourceProvider::ResourceId id, boo
     resource->enableReadLockFences = enable;
 }
 
+void ResourceProvider::setOffscreenContextProvider(scoped_refptr<ui::ContextProvider> offscreenContextProvider) {
+  if (offscreenContextProvider)
+      offscreenContextProvider->BindToCurrentThread();
+  m_offscreenContextProvider = offscreenContextProvider;
+}
+
 }  // namespace cc