Update Linux to use scoped_refptr<T>::get() rather than implicit "operator T*"

cc/layers/texture_layer.h

Index: cc/layers/texture_layer.h
diff --git a/cc/layers/texture_layer.h b/cc/layers/texture_layer.h
index cbc42ceca086e9b30a78844854dce8d971dc1524..6be2a017e710342c6e3712c074aba3d4214598d1 100644
--- a/cc/layers/texture_layer.h
+++ b/cc/layers/texture_layer.h
@@ -94,7 +94,7 @@ class CC_EXPORT TextureLayer : public Layer {
      public:
       explicit MainThreadReference(MailboxHolder* holder);
       ~MainThreadReference();
-      MailboxHolder* holder() { return holder_; }
+      MailboxHolder* holder() { return holder_.get(); }
 
      private:
       scoped_refptr<MailboxHolder> holder_;