Avoid exposing cc::Layer tree to CompositorProxy

third_party/WebKit/Source/core/dom/CompositorProxy.h

Index: third_party/WebKit/Source/core/dom/CompositorProxy.h
diff --git a/third_party/WebKit/Source/core/dom/CompositorProxy.h b/third_party/WebKit/Source/core/dom/CompositorProxy.h
index ee73842cfc8f7f33c74740a3e46961439bf2ea1a..84e4d47ae7b911195cd07cd85aea51daf008f76d 100644
--- a/third_party/WebKit/Source/core/dom/CompositorProxy.h
+++ b/third_party/WebKit/Source/core/dom/CompositorProxy.h
@@ -39,6 +39,7 @@ class CORE_EXPORT CompositorProxy final
   DECLARE_TRACE();
 
   uint64_t ElementId() const { return element_id_; }
+  uint64_t ProxyId() const { return proxy_id_; }
   uint32_t CompositorMutableProperties() const {
     return compositor_mutable_properties_;
   }
@@ -72,6 +73,7 @@ class CORE_EXPORT CompositorProxy final
                                   ExceptionState&) const;
   void DisconnectInternal();
 
+  const uint64_t proxy_id_ = 0;
   const uint64_t element_id_ = 0;
   const uint32_t compositor_mutable_properties_ = 0;