Don't swap out the old RenderFrameHost until the new one commits.

content/renderer/render_widget.h

 // Copyright (c) 2012 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.
 
 #ifndef CONTENT_RENDERER_RENDER_WIDGET_H_
 #define CONTENT_RENDERER_RENDER_WIDGET_H_
 
 #include <deque>
 #include <map>
 
@@ skipping 316 matching lines @@
 
   // Finishes creation of a pending view started with Init.
   void CompleteInit();
 
   // Sets whether this RenderWidget has been swapped out to be displayed by
   // a RenderWidget in a different process.  If so, no new IPC messages will be
   // sent (only ACKs) and the process is free to exit when there are no other
   // active RenderWidgets.
   void SetSwappedOut(bool is_swapped_out);
 
+  // Allows the process to exit once the unload handler has finished, if there
+  // are no other active RenderWidgets.
+  void WasSwappedOut();
+
   void FlushPendingInputEventAck();
   void DoDeferredClose();
   void DoDeferredSetWindowRect(const blink::WebRect& pos);
 
   // Resizes the render widget.
   void Resize(const gfx::Size& new_size,
               const gfx::Size& physical_backing_size,
               float overdraw_bottom_height,
               const gfx::Size& visible_viewport_size,
               const gfx::Rect& resizer_rect,
@@ skipping 17 matching lines @@
   void OnCursorVisibilityChange(bool is_visible);
   void OnMouseCaptureLost();
   virtual void OnSetFocus(bool enable);
   virtual void OnClose();
   void OnCreatingNewAck();
   virtual void OnResize(const ViewMsg_Resize_Params& params);
   void OnChangeResizeRect(const gfx::Rect& resizer_rect);
   virtual void OnWasHidden();
   virtual void OnWasShown(bool needs_repainting,
                           const ui::LatencyInfo& latency_info);
-  virtual void OnWasSwappedOut();
   void OnCreateVideoAck(int32 video_id);
   void OnUpdateVideoAck(int32 video_id);
   void OnRequestMoveAck();
   void OnSetInputMethodActive(bool is_active);
   void OnCandidateWindowShown();
   void OnCandidateWindowUpdated();
   void OnCandidateWindowHidden();
   virtual void OnImeSetComposition(
       const base::string16& text,
       const std::vector<blink::WebCompositionUnderline>& underlines,
@@ skipping 355 matching lines @@
   ui::MenuSourceType context_menu_source_type_;
   bool has_host_context_menu_location_;
   gfx::Point host_context_menu_location_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderWidget);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_RENDER_WIDGET_H_