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..392cdf721fbf6d131669504392fcd11907caa437 100644
--- a/cc/resource_provider.cc
+++ b/cc/resource_provider.cc
@@ -11,6 +11,7 @@
 #include "base/stl_util.h"
 #include "base/string_split.h"
 #include "base/string_util.h"
+#include "cc/context_provider.h"
 #include "cc/gl_renderer.h" // For the GLC() macro.
 #include "cc/platform_color.h"
 #include "cc/texture_uploader.h"
@@ -1124,4 +1125,10 @@ void ResourceProvider::enableReadLockFences(ResourceProvider::ResourceId id, boo
     resource->enableReadLockFences = enable;
 }
 
+void ResourceProvider::setOffscreenContextProvider(scoped_refptr<cc::ContextProvider> offscreenContextProvider) {
+  if (offscreenContextProvider)
+      offscreenContextProvider->BindToCurrentThread();
+  m_offscreenContextProvider = offscreenContextProvider;
+}
+
 }  // namespace cc