Cleanup ChildFrameCompositingHelper on destruction.

BUG=448507

Review URL: https://codereview.chromium.org/857643002

Cr-Commit-Position: refs/heads/master@{#314426}

content/renderer/child_frame_compositing_helper.cc

@@ -61,7 +61,10 @@ ChildFrameCompositingHelper::ChildFrameCompositingHelper(
       render_frame_proxy_(render_frame_proxy),
       frame_(frame) {}
 
-ChildFrameCompositingHelper::~ChildFrameCompositingHelper() {}
+ChildFrameCompositingHelper::~ChildFrameCompositingHelper() {
+  if (resource_collection_.get())
+    resource_collection_->SetClient(NULL);
+}
 
 BrowserPluginManager* ChildFrameCompositingHelper::GetBrowserPluginManager() {
   if (!browser_plugin_)