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

third_party/WebKit/Source/core/frame/LocalFrame.h

Index: third_party/WebKit/Source/core/frame/LocalFrame.h
diff --git a/third_party/WebKit/Source/core/frame/LocalFrame.h b/third_party/WebKit/Source/core/frame/LocalFrame.h
index 4c00a5b8f81b6c7df73b21246a5d0656f136b6f6..984e985fdf9018faa6f10b6d46ea8d579182cd08 100644
--- a/third_party/WebKit/Source/core/frame/LocalFrame.h
+++ b/third_party/WebKit/Source/core/frame/LocalFrame.h
@@ -81,6 +81,7 @@ class PluginData;
 class ScriptController;
 class SpellChecker;
 class WebFrameScheduler;
+class WebPluginContainerBase;
 class WebURLLoader;
 
 extern template class CORE_EXTERN_TEMPLATE_EXPORT Supplement<LocalFrame>;
@@ -244,6 +245,12 @@ class CORE_EXPORT LocalFrame final : public Frame,
   // for adding a callback multiple times.
   static void RegisterInitializationCallback(FrameInitCallback);
 
+  // If the frame hosts a PluginDocument, this method returns the
+  // WebPluginContainerBase that hosts the plugin. If the provided node is a
+  // plugin, then it returns its WebPluginContainerBase. Otherwise, uses the
+  // currently focused element (if any).

[haraken, 2017/05/22 04:51:44]

This looks like a weird semantics. Can we drop the part after "If the provided
node..." in a follow-up CL?

Alternately we can just make the caller site to query the focused element and
call Node::GetWebPluginContainerBase when LocalFrame::GetWebPluginContainerBase
returns nullptr. It looks weird to hide the logic in
LocalFrame::GetWebPluginContainerBase.

[dcheng, 2017/05/22 09:48:29]

I agree it's a bit confusing (which is why I was hoping we didn't have to plumb
a Node in at all). But I'm not sure if making current callsites explicitly grab
the focused node is better as it's called in a fair number of different places.

[slangley, 2017/05/22 23:53:25]

I added a TODO and will followup with a CL to address this.

+  WebPluginContainerBase* GetWebPluginContainerBase(Node* = nullptr) const;
+
  private:
   friend class FrameNavigationDisabler;