Enable swapping a frame back in to its parent process

content/browser/frame_host/frame_tree.cc

Index: content/browser/frame_host/frame_tree.cc
diff --git a/content/browser/frame_host/frame_tree.cc b/content/browser/frame_host/frame_tree.cc
index 077cf08b1681ac1329ccebe28055b32546e186ee..6b9c0897cf80a271ec7a6d7b5eaa65cfadc2a06c 100644
--- a/content/browser/frame_host/frame_tree.cc
+++ b/content/browser/frame_host/frame_tree.cc
@@ -59,6 +59,11 @@ bool CreateProxyForSiteInstance(FrameTreeNode* source_node,
   if (source_node == node)
     return true;
 
+  // If a given frame host has the same SiteInstance, no proxy is needed.
+  if (node->render_manager()->current_frame_host()->GetSiteInstance() ==

[Nate Chapin, 2014/09/30 21:44:47]

If we're swapping a LocalFrame in place of a RemoteFrame, there is at least one
LocalFrame in the target renderer. Don't create a proxy if one isn't needed.

[Charlie Reis, 2014/09/30 23:02:43]

Hmm, it feels wrong to be calling this function on nodes that already have a
frame in this SiteInstance, but maybe that's how it's written.  Nasko, do you
think there's a cleaner way to handle this?

[nasko, 2014/10/08 16:42:58]

CreateRenderFrameProxy already takes care of the case where there is a proxy for
this SiteInstance.
We shouldn't be creating a proxy for the SiteInstance of the current RFH. What
code path triggers that?

[Nate Chapin, 2014/10/08 20:30:05]

CreateRenderFrameProxy indeed correctly handles when a proxy exists for this
SiteInstance, but it starts by CHECKing that we never ask to create a proxy in
the same SiteInstance that we're navigating in. I guess that CHECK is no longer
valid?

[Charlie Reis, 2014/10/08 20:49:50]

I keep hitting that CHECK as well.  I think Nasko has a patch in progress to fix
it, blocked on some UaF issues.

[nasko, 2014/10/08 20:56:44]

I think the CHECK should be there and is valid. Charlie is correct that I have a
CL in place for that. See if patching it in will help:
https://codereview.chromium.org/600483003/

+      instance)
+    return true;
+
   node->render_manager()->CreateRenderFrameProxy(instance.get());
   return true;
 }