Move the logic to retrieve the WebPluginContainer to LocalFrame and Node.

third_party/WebKit/Source/web/WebPluginContainerImpl.h

Index: third_party/WebKit/Source/web/WebPluginContainerImpl.h
diff --git a/third_party/WebKit/Source/web/WebPluginContainerImpl.h b/third_party/WebKit/Source/web/WebPluginContainerImpl.h
index 1346b023ee0d5e61a3e35e42f996ff369620f7de..f3d3b9adc127a5c0ce97af8db0d5959fd3393d3f 100644
--- a/third_party/WebKit/Source/web/WebPluginContainerImpl.h
+++ b/third_party/WebKit/Source/web/WebPluginContainerImpl.h
@@ -175,6 +175,10 @@ class WEB_EXPORT WebPluginContainerImpl final : public WebPluginContainerBase {
   void DidFinishLoading() override;
   void DidFailLoading(const ResourceError&) override;
 
+  WebPluginContainerBase* GetWebPluginContainerBase() const override {
+    return const_cast<WebPluginContainerImpl*>(this);
+  }
+
   DECLARE_VIRTUAL_TRACE();
   // USING_PRE_FINALIZER does not allow for virtual dispatch from the finalizer
   // method. Here we call Dispose() which does the correct virtual dispatch.