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

cc/trees/layer_tree_impl.h

Index: cc/trees/layer_tree_impl.h
diff --git a/cc/trees/layer_tree_impl.h b/cc/trees/layer_tree_impl.h
index e21b1c87435452ca3bf8bfc05cb60854613e0314..67b7839b39eb10ff276f4deadcc4856328a7cbd7 100644
--- a/cc/trees/layer_tree_impl.h
+++ b/cc/trees/layer_tree_impl.h
@@ -73,7 +73,7 @@ class CC_EXPORT LayerTreeImpl {
   // ---------------------------------------------------------------------------
   const LayerTreeSettings& settings() const;
   const RendererCapabilitiesImpl& GetRendererCapabilities() const;
-  ContextProvider* context_provider() const;
+  scoped_refptr<ContextProvider> context_provider() const;

[danakj, 2014/08/25 20:25:01]

I don't think we want to add references to this thing freely. What code is
requiring this?

[dcheng, 2014/08/25 20:56:58]

This is the logic to try to catch temporary scoped_refptrs being returned
kicking in again.

Foo* foo() { return ReturnsScopedRefPtr(); } would be potentially unsafe.

But I've reverted this as well and just changed the implementation to call
.get().

   OutputSurface* output_surface() const;
   ResourceProvider* resource_provider() const;
   TileManager* tile_manager() const;