Ensure that the page id assignment IPC is sent.

content/renderer/render_frame_impl.cc

Index: content/renderer/render_frame_impl.cc
diff --git a/content/renderer/render_frame_impl.cc b/content/renderer/render_frame_impl.cc
index 0773d410a668139f071d9f8a13140f3ce6ba9f59..493f3c0a2c5602f02fd0b73b70e3fdfe3e0c5b3e 100644
--- a/content/renderer/render_frame_impl.cc
+++ b/content/renderer/render_frame_impl.cc
@@ -2287,7 +2287,9 @@ void RenderFrameImpl::didCommitProvisionalLoad(
     }
   }
 
-  Send(new FrameHostMsg_DidAssignPageId(routing_id_, render_view_->page_id_));
+  bool sent = Send(
+      new FrameHostMsg_DidAssignPageId(routing_id_, render_view_->page_id_));
+  CHECK(sent);  // http://crbug.com/407376
 
   FOR_EACH_OBSERVER(RenderViewObserver, render_view_->observers_,
                     DidCommitProvisionalLoad(frame, is_new_navigation));