Support cross-process navigations in a single subframe RenderFrameHost.

content/browser/frame_host/frame_tree.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/frame_host/frame_tree.h"
 
 #include <queue>
 
 #include "base/bind.h"
 #include "base/callback.h"
@@ skipping 178 matching lines @@
 
   render_view_host_map_[site_instance->GetId()] =
       RenderViewHostRefCount(rvh, 0);
   return rvh;
 }
 
 RenderViewHostImpl* FrameTree::GetRenderViewHostForSubFrame(
     SiteInstance* site_instance) {
   RenderViewHostMap::iterator iter =
       render_view_host_map_.find(site_instance->GetId());
-  CHECK(iter != render_view_host_map_.end());
+  // TODO(creis): Mirror the frame tree so this check can't fail.
+  if (iter == render_view_host_map_.end())
+    return NULL;
   RenderViewHostRefCount rvh_refcount = iter->second;
   return rvh_refcount.first;
 }
 
 void FrameTree::RegisterRenderFrameHost(
     RenderFrameHostImpl* render_frame_host) {
   SiteInstance* site_instance =
       render_frame_host->render_view_host()->GetSiteInstance();
   RenderViewHostMap::iterator iter =
       render_view_host_map_.find(site_instance->GetId());
@@ skipping 22 matching lines @@
   }
 }
 
 FrameTreeNode* FrameTree::FindByFrameID(int64 frame_id) {
   FrameTreeNode* node = NULL;
   ForEach(base::Bind(&FrameTreeNodeForFrameId, frame_id, &node));
   return node;
 }
 
 }  // namespace content