Ensure RenderViewHost is not shut down until a screenshot of the page is taken.

content/browser/renderer_host/render_view_host_impl.h

Index: content/browser/renderer_host/render_view_host_impl.h
diff --git a/content/browser/renderer_host/render_view_host_impl.h b/content/browser/renderer_host/render_view_host_impl.h
index 050edc030717b1358ad23ad23748bb78afd0d60d..b9e0569dcb9aeeb5b423aa9a4d9cb87229e1df21 100644
--- a/content/browser/renderer_host/render_view_host_impl.h
+++ b/content/browser/renderer_host/render_view_host_impl.h
@@ -230,6 +230,11 @@ class CONTENT_EXPORT RenderViewHostImpl
       const WebPreferences& prefs) OVERRIDE;
   virtual void GetAudioOutputControllers(
       const GetAudioOutputControllersCallback& callback) const OVERRIDE;
+  virtual void CopyFromBackingStore(
+      const gfx::Rect& src_rect,
+      const gfx::Size& accelerated_dst_size,
+      const base::Callback<void(bool, const SkBitmap&)>& callback,
+      const SkBitmap::Config& bitmap_config) OVERRIDE;
 
 #if defined(OS_ANDROID)
   virtual void ActivateNearestFindResult(int request_id,
@@ -243,6 +248,11 @@ class CONTENT_EXPORT RenderViewHostImpl
   virtual void SetWebUIHandle(mojo::ScopedMessagePipeHandle handle) OVERRIDE;
 #endif
 
+  void CopyFromBackingStoreCallback(
+      const base::Callback<void(bool, const SkBitmap&)>& callback,
+      bool success,
+      const SkBitmap& bitmap);
+
   void set_delegate(RenderViewHostDelegate* d) {
     CHECK(d);  // http://crbug.com/82827
     delegate_ = d;
@@ -720,11 +730,22 @@ class CONTENT_EXPORT RenderViewHostImpl
   // TODO(nasko): Move to RenderFrameHost, as this is per-frame state.
   scoped_ptr<TimeoutMonitor> unload_event_monitor_timeout_;
 
-  // Called after receiving the SwapOutACK when the RVH is in state pending
-  // shutdown. Also called if the unload timer times out.
+  // Called after receiving the SwapOutACK and completing outstanding copy
+  // requests when the RVH is in state pending shutdown. Also called if the
+  // unload timer times out.
   // TODO(nasko): Move to RenderFrameHost, as this is per-frame state.
   base::Closure pending_shutdown_on_swap_out_;
 
+  // Set to true if pending_shutdown_on_swap_out_ is not invoked upon receiving
+  // the SwapOutACK because of outstanding copy requests. In this case
+  // pending_shutdown_on_swap_out_ gets called when the copy requests complete.
+  bool pending_shutdown_on_copy_requests_done_;
+
+  // Stores the number of the outstanding copy requests (see
+  // CopyFromBackingStore()). If the host gets swapped out with outstanding copy
+  // requests, we delay its shutdown until the copy requests complete.
+  int copy_requests_;
+
   base::WeakPtrFactory<RenderViewHostImpl> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderViewHostImpl);