Require a process ID when looking up RFHs by FrameTreeNode ID.

content/public/browser/navigation_handle.h

Index: content/public/browser/navigation_handle.h
diff --git a/content/public/browser/navigation_handle.h b/content/public/browser/navigation_handle.h
index 684fd26aa145b62a67505afb0e6db0e3a5ab4456..13c647d63de2c33a17055f5bafdfd478e2438e23 100644
--- a/content/public/browser/navigation_handle.h
+++ b/content/public/browser/navigation_handle.h
@@ -82,9 +82,10 @@ class CONTENT_EXPORT NavigationHandle {
   // stays constant for the lifetime of the frame.
   virtual int GetFrameTreeNodeId() = 0;
 
-  // Returns the FrameTreeNode ID for the parent frame. If this navigation is
-  // taking place in the main frame, the value returned is -1.
-  virtual int GetParentFrameTreeNodeId() = 0;
+  // Returns the RenderFrameHost for the parent frame, or nullptr if this
+  // navigation is taking place in the main frame. This value will not change
+  // during a navigation.
+  virtual RenderFrameHost* GetParentFrame() = 0;

[Devlin, 2017/05/02 02:04:29]

If we were worried before about callers storing the render frame tree node id
and not expected a change, is this better?  Is it safer to store a raw ptr to a
RenderFrameHost?

[Charlie Reis, 2017/05/04 16:29:58]

Yes, since the parent RenderFrameHost doesn't change during the navigation, and
the navigation would be canceled if it did.  (More specifically, a cross-process
navigation in the parent FrameTreeNode will synchronously delete the subtree of
FrameTreeNodes and RenderFrameHosts, which will delete any of their
NavigationHandles as well.  Same if the parent is detached or closed.)
I don't think this should be a problem, given that we already expose a raw
pointer to this frame's RenderFrameHost below (after the NavigationHandle is
ready to commit).  Exposing the FTN ID here just seemed to be a hurdle to the
actual uses, which wasn't adding much value in the NavigationHandle case when
there's no risk of it changing.

 
   // The WebContents the navigation is taking place in.
   WebContents* GetWebContents();