Add UMA counter for hung renderers on cross-site navigation.

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 bfb34bca25567e6362b7193b8329d0367e7cf7de..f23fb6f839db8e1df7f0175590d219fbb8118347 100644
--- a/content/browser/renderer_host/render_view_host_impl.h
+++ b/content/browser/renderer_host/render_view_host_impl.h
@@ -302,8 +302,9 @@ class CONTENT_EXPORT RenderViewHostImpl
   // of the parameters.
   void SwapOut(int new_render_process_host_id, int new_request_id);
 
-  // Called by ResourceDispatcherHost after the SwapOutACK is received.
-  void OnSwapOutACK();
+  // Called by ResourceDispatcherHost after the SwapOutACK is received or the
+  // response times out.
+  void OnSwapOutACK(bool timed_out);
 
   // Called to notify the renderer that it has been visibly swapped out and
   // replaced by another RenderViewHost, after an earlier call to SwapOut.
@@ -636,6 +637,9 @@ class CONTENT_EXPORT RenderViewHostImpl
   // is_waiting_for_beforeunload_ack_, unload_ack_is_for_cross_site_transition_.
   bool is_waiting_for_unload_ack_;
 
+  // Set to true when waiting for ViewHostMsg_SwapOut_ACK has timed out.
+  bool has_timed_out_on_unload_;
+
   // Valid only when is_waiting_for_beforeunload_ack_ or
   // is_waiting_for_unload_ack_ is true.  This tells us if the unload request
   // is for closing the entire tab ( = false), or only this RenderViewHost in