Enable swapping a frame back in to its parent process

content/browser/frame_host/render_frame_host_impl.cc

Index: content/browser/frame_host/render_frame_host_impl.cc
diff --git a/content/browser/frame_host/render_frame_host_impl.cc b/content/browser/frame_host/render_frame_host_impl.cc
index 1f228805e7651e4c4876b0ca92393e503dc9ec18..c4ebf25f63d2aa4b676b2d8d8291422bd9800ca9 100644
--- a/content/browser/frame_host/render_frame_host_impl.cc
+++ b/content/browser/frame_host/render_frame_host_impl.cc
@@ -577,7 +577,11 @@ bool RenderFrameHostImpl::CreateRenderFrame(int parent_routing_id) {
 
   DCHECK(GetProcess()->HasConnection());
 
-  Send(new FrameMsg_NewFrame(routing_id_, parent_routing_id));
+  RenderFrameProxyHost* proxy = frame_tree_node_->render_manager()->
+      GetRenderFrameProxyHost(GetSiteInstance());

[nasko, 2014/10/27 22:52:54]

This type of logic should be in RenderFrameHostManager. That would mean that we
need to plumb it all the way through WebContentsImpl. I'm a bit torn on what the
right approach is, so let's hear what Charlie has to say.

Also, we have an invariant that we want to always uphold - there should be no
proxy for the same SiteInstance as the active RFH. What we are doing here is
exactly against it : ), so let's add a CHECK to ensure that this is the pending
RFH and not the current one.

[Charlie Reis, 2014/10/28 16:38:29]

+1.  This should get passed in from RFHM via WebContentsImpl.
Yeah, I was confused by this.  We only want it to be a real value when we're
swapping from a proxy to an active frame.  It's awkward to CHECK that we're the
pending RFH, though, since that requires asking the RFHM (not ideal, as above). 
Instead, let's just document it with a comment.

[Nate Chapin, 2014/10/28 19:59:19]

Done.

+  int proxy_routing_id = proxy ? proxy->GetRoutingID() : MSG_ROUTING_NONE;
+
+  Send(new FrameMsg_NewFrame(routing_id_, parent_routing_id, proxy_routing_id));
 
   // The renderer now has a RenderFrame for this RenderFrameHost.  Note that
   // this path is only used for out-of-process iframes.  Main frame RenderFrames