Make RenderFrameHostManager swap RenderFrameHosts, not RenderViewHosts.

content/test/test_render_frame_host.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/test/test_render_frame_host.h"
 
+#include "content/browser/frame_host/frame_tree.h"
+#include "content/test/test_render_view_host.h"
+
 namespace content {
 
 TestRenderFrameHost::TestRenderFrameHost(RenderViewHostImpl* render_view_host,
                                          RenderFrameHostDelegate* delegate,
                                          FrameTree* frame_tree,
                                          FrameTreeNode* frame_tree_node,
                                          int routing_id,
                                          bool is_swapped_out)
     : RenderFrameHostImpl(render_view_host,
                           delegate,
                           frame_tree,
                           frame_tree_node,
                           routing_id,
-                          is_swapped_out) {}
+                          is_swapped_out) {
+  // Allow TestRenderViewHosts to easily access their main frame RFH.
+  if (frame_tree_node == frame_tree->root()) {
+    static_cast<TestRenderViewHost*>(render_view_host)->
+        set_main_render_frame_host(this);
+  }
+}
 
 TestRenderFrameHost::~TestRenderFrameHost() {}
 
 }  // namespace content