Remove implicit conversions from scoped_refptr to T* in cc/trees/

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index 6d2d88d57db2c619b2b954806c31460215eaa0e1..7cd53d2f47d9cc82f83ec7da94451973a519ddc3 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -657,7 +657,7 @@ const RendererCapabilitiesImpl& LayerTreeImpl::GetRendererCapabilities() const {
   return layer_tree_host_impl_->GetRendererCapabilities();
 }
 
-ContextProvider* LayerTreeImpl::context_provider() const {
+scoped_refptr<ContextProvider> LayerTreeImpl::context_provider() const {
   return output_surface()->context_provider();
 }