Use FrameTreeNode ID as frameId in extension APIs

content/public/browser/render_frame_host.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_PUBLIC_BROWSER_RENDER_FRAME_HOST_H_
 #define CONTENT_PUBLIC_BROWSER_RENDER_FRAME_HOST_H_
 
 #include <string>
 
 #include "base/callback_forward.h"
@@ skipping 46 matching lines @@
   virtual SiteInstance* GetSiteInstance() = 0;
 
   // Returns the process for this frame.
   virtual RenderProcessHost* GetProcess() = 0;
 
   // Returns the current RenderFrameHost of the parent frame, or nullptr if
   // there is no parent. The result may be in a different process than the
   // current RenderFrameHost.
   virtual RenderFrameHost* GetParent() = 0;
 
+  // Returns the FrameTreeNode ID for this frame.

[Charlie Reis, 2015/11/06 23:13:16]

Nasko brings up a good point that we may not want to call this
"GetFrameTreeNodeID," since there's no FrameTreeNode in the public API... 
Sadly, "frame ID" is slightly ambiguous since we already have render_frame_id in
some APIs (which confusingly refers to RenderFrame routing ID).

I'm not sure if there's a better option-- GetFrameID (and bite the bullet vs
render_frame_id) vs somehow explaining what GetFrameTreeNodeID means vs
something else?

Either way, we should elaborate on what this concept means here, since there's
no other explanation in the public API.  In other words, that it is a stable
identifier for a frame even after it does cross-process navigations that switch
its RenderFrameHost.

+  virtual int GetFrameTreeNodeID() = 0;

[nasko, 2015/11/06 23:28:27]

Let's call this GetFrameId(). FrameTreeNode is not a concept exposed outside of
content/ and shouldn't be leaked, even through naming of methods.
Also, include another sentence which describes the meaning of this id - a unique
ID for this frame, which will not change even across cross-process navigations.

[robwu, 2015/11/07 00:23:40]

It is very likely that GetFrameId is confused with the RenderFrame routing ID,
so we need a name that is a bit more specific than GetFrameId.

+
   // Returns the assigned name of the frame, the name of the iframe tag
   // declaring it. For example, <iframe name="framename">[...]</iframe>. It is
   // quite possible for a frame to have no name, in which case GetFrameName will
   // return an empty string.
   virtual const std::string& GetFrameName() = 0;
 
   // Returns true if the frame is out of process.
   virtual bool IsCrossProcessSubframe() = 0;
 
   // Returns the last committed URL of the frame.
@@ skipping 73 matching lines @@
 
  private:
   // This interface should only be implemented inside content.
   friend class RenderFrameHostImpl;
   RenderFrameHost() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_RENDER_FRAME_HOST_H_