[DRAFT] Create RenderFrameHostManager.

content/browser/frame_host/navigator_impl.cc

Index: content/browser/frame_host/navigator_impl.cc
diff --git a/content/browser/frame_host/navigator_impl.cc b/content/browser/frame_host/navigator_impl.cc
index 6cc9dad14885e502b697660e469fc0f8a1a482f5..645988a7e20437dba90299559cb812cc4b6febf5 100644
--- a/content/browser/frame_host/navigator_impl.cc
+++ b/content/browser/frame_host/navigator_impl.cc
@@ -38,15 +38,20 @@ void NavigatorImpl::DidStartProvisionalLoad(
   RenderProcessHost* render_process_host = render_frame_host->GetProcess();
   RenderViewHost::FilterURL(render_process_host, false, &validated_url);
 
+  // TODO(creis): This is a hack for now, until we mirror the frame tree and do
+  // cross-process subframe navigations in actual subframes.  As a result, we
+  // can currently only support a single cross-process subframe per RVH.
+  NavigationEntryImpl* pending_entry =
+      NavigationEntryImpl::FromNavigationEntry(controller_->GetPendingEntry());
+  if (pending_entry && pending_entry->frame_tree_node_id() != -1)
+    is_main_frame = false;
+
   if (is_main_frame) {
     // If there is no browser-initiated pending entry for this navigation and it
     // is not for the error URL, create a pending entry using the current
     // SiteInstance, and ensure the address bar updates accordingly.  We don't
     // know the referrer or extra headers at this point, but the referrer will
     // be set properly upon commit.
-    NavigationEntryImpl* pending_entry =
-        NavigationEntryImpl::FromNavigationEntry(
-            controller_->GetPendingEntry());
     bool has_browser_initiated_pending_entry = pending_entry &&
         !pending_entry->is_renderer_initiated();
     if (!has_browser_initiated_pending_entry && !is_error_page) {