[DRAFT] Create RenderFrameHostManager.

content/browser/frame_host/render_frame_host_impl.h

Index: content/browser/frame_host/render_frame_host_impl.h
diff --git a/content/browser/frame_host/render_frame_host_impl.h b/content/browser/frame_host/render_frame_host_impl.h
index dbe8972e2ac3a120d554c8a24fde378d49be2942..108c1f278e7dfffa68ecfae4ac5374b26fb6afad 100644
--- a/content/browser/frame_host/render_frame_host_impl.h
+++ b/content/browser/frame_host/render_frame_host_impl.h
@@ -59,8 +59,13 @@ class CONTENT_EXPORT RenderFrameHostImpl : public RenderFrameHost {
 
   bool is_swapped_out() { return is_swapped_out_; }
 
-  // TODO(nasko): This should be removed and replaced by RenderProcessHost.
-  RenderViewHostImpl* render_view_host_;  // Not owned.
+  // For now, RenderFrameHosts indirectly keep RenderViewHosts alive via the
+  // refcount on FrameTree.  This allows each RenderFrameHostManager to just
+  // care about RenderFrameHosts, while ensuring we have a RenderViewHost for
+  // each RenderFrameHost.
+  // TODO(creis): RenderViewHost will eventually go away and be replaced with
+  // some form of page context.
+  RenderViewHostImpl* render_view_host_;
 
   // Reference to the whole frame tree that this RenderFrameHost belongs too.
   // Allows this RenderFrameHost to add and remove nodes in response to