Update a comment with a link to a historic source.

content/browser/frame_host/navigation_controller_impl.cc

Index: content/browser/frame_host/navigation_controller_impl.cc
diff --git a/content/browser/frame_host/navigation_controller_impl.cc b/content/browser/frame_host/navigation_controller_impl.cc
index f4f184ba42b9889896b76abd0b6682735ed53464..a436d79ff419d7526bafd98fa34b86697468ad03 100644
--- a/content/browser/frame_host/navigation_controller_impl.cc
+++ b/content/browser/frame_host/navigation_controller_impl.cc
@@ -1215,7 +1215,12 @@ void NavigationControllerImpl::RendererDidNavigateNewSubframe(
     const FrameHostMsg_DidCommitProvisionalLoad_Params& params) {
   if (ui::PageTransitionCoreTypeIs(params.transition,
                                    ui::PAGE_TRANSITION_AUTO_SUBFRAME)) {
-    // This is not user-initiated. Ignore.
+    // The old comment here was "This is not user-initiated. Ignore." This is a
+    // weird scenario, where we've determined that this was a new subframe
+    // navigation but say "never mind" based on a flag from the renderer.

[Charlie Reis, 2015/01/15 22:12:09]

Maybe I misunderstood this case before, but I thought it was used for the first
navigation in a newly created iframe, which meant it shouldn't create a new
NavigationEntry.  That seems like a pretty standard case to me.

If so, I'm fine with updating the comment to be a bit more explicit about that,
though.

[Avi (use Gerrit), 2015/01/15 22:16:52]

Will investigate.

[Avi (use Gerrit), 2015/01/16 21:06:26]

Isn't that what RendererDidNavigateAutoSubframe is for, though?

I'm rebuilding and looking at this.

+    //
+    // This dates back to http://crrev.com/115919 and the handling of immediate

[Charlie Reis, 2015/01/15 22:12:09]

This revision is a DEPS roll.  Did you mean http://crrev.com/18373 (from
https://codereview.chromium.org/115919)?

That CL is indeed weird and troubling, but thankfully it doesn't look like most
of its time-based ignore-redirect logic is still around.

[Avi (use Gerrit), 2015/01/15 22:16:52]

Yes. I used the auto-shortener and am bummed that it screwed up the URL.
Yeah.

+    // redirects. TODO(avi): Is this still valid?
     DiscardNonCommittedEntriesInternal();
     return;
   }