compositor-worker: Add CompositorProxyClient worker client of CompositorWorker.

third_party/WebKit/Source/web/WebViewImpl.h

Index: third_party/WebKit/Source/web/WebViewImpl.h
diff --git a/third_party/WebKit/Source/web/WebViewImpl.h b/third_party/WebKit/Source/web/WebViewImpl.h
index 6c951efa8a18064d8102ae9893c6cd1ae9230519..8bb5a8eff7c5732f4aced284a4164ba5dc0f603d 100644
--- a/third_party/WebKit/Source/web/WebViewImpl.h
+++ b/third_party/WebKit/Source/web/WebViewImpl.h
@@ -87,6 +87,7 @@ class WebLayerTreeView;
 class WebLocalFrame;
 class WebLocalFrameImpl;
 class WebImage;
+class CompositorMutatorImpl;
 class WebPagePopupImpl;
 class WebPlugin;
 class WebRemoteFrame;
@@ -502,6 +503,7 @@ public:
     void forceNextWebGLContextCreationToFail() override;
     void forceNextDrawingBufferCreationToFail() override;
 
+    CompositorProxyClient* createCompositorProxyClient();
     IntSize mainFrameSize();
     WebDisplayMode displayMode() const { return m_displayMode; }