Use FrameTreeNode ID as frameId in extension APIs

content/public/browser/render_frame_host.h

Index: content/public/browser/render_frame_host.h
diff --git a/content/public/browser/render_frame_host.h b/content/public/browser/render_frame_host.h
index 7e769cb154ad7754de70a7559025c733556dfd8f..26853765c8649e26c9a7ca835407ca53f5ad949f 100644
--- a/content/public/browser/render_frame_host.h
+++ b/content/public/browser/render_frame_host.h
@@ -35,6 +35,10 @@ class CONTENT_EXPORT RenderFrameHost : public IPC::Listener,
   // Returns nullptr if the IDs do not correspond to a live RenderFrameHost.
   static RenderFrameHost* FromID(int render_process_id, int render_frame_id);
 
+  // Returns the RenderFrameHost that hosts the frame identified by the given
+  // FrameTreeNode ID. Returns nullptr if not found.
+  static RenderFrameHost* FromFrameTreeNodeID(int frame_tree_node_id);
+
   // Globally allows for injecting JavaScript into the main world. This feature
   // is present only to support Android WebView and must not be used in other
   // configurations.
@@ -64,6 +68,13 @@ class CONTENT_EXPORT RenderFrameHost : public IPC::Listener,
   // current RenderFrameHost.
   virtual RenderFrameHost* GetParent() = 0;
 
+  // Returns the RenderFrameHost for the given FrameTreeNode ID if it is the
+  // frame itself or a child of this frame.
+  virtual RenderFrameHost* FindByFrameTreeNodeID(int frame_tree_node_id) = 0;
+
+  // Returns the FrameTreeNode ID for this frame.
+  virtual int GetFrameTreeNodeID() = 0;
+
   // 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