Remove WebLayerTreeView::finishAllRendering(), nothing uses it.

public/platform/WebLayerTreeView.h

Index: public/platform/WebLayerTreeView.h
diff --git a/public/platform/WebLayerTreeView.h b/public/platform/WebLayerTreeView.h
index 67a11e23a4c616277f53bd5869a5f127bdabf88c..28a880fc66ddb80bbf890b341403bc7f78f9677a 100644
--- a/public/platform/WebLayerTreeView.h
+++ b/public/platform/WebLayerTreeView.h
@@ -128,10 +128,6 @@ public:
     // object alive until it is called.
     virtual void compositeAndReadbackAsync(WebCompositeAndReadbackAsyncCallback*) { }
 
-    // Blocks until the most recently composited frame has finished rendering on the GPU.
-    // This can have a significant performance impact and should be used with care.
-    virtual void finishAllRendering() { }
-
     // Prevents updates to layer tree from becoming visible.
     virtual void setDeferCommits(bool deferCommits) { }