PlzNavigate: fix flaky TabManagerTest.TabManagerBasics browser test.

content/browser/web_contents/web_contents_impl.cc

Index: content/browser/web_contents/web_contents_impl.cc
diff --git a/content/browser/web_contents/web_contents_impl.cc b/content/browser/web_contents/web_contents_impl.cc
index 46a226f7c67434387fa3d2765c8253817d999130..d6a4f94c90a6b273276b6b3f997db6ddabda43d9 100644
--- a/content/browser/web_contents/web_contents_impl.cc
+++ b/content/browser/web_contents/web_contents_impl.cc
@@ -674,9 +674,15 @@ bool WebContentsImpl::OnMessageReceived(RenderViewHost* render_view_host,
                                         RenderFrameHost* render_frame_host,
                                         const IPC::Message& message) {
   DCHECK(render_view_host || render_frame_host);
-  if (GetWebUI() &&
-      static_cast<WebUIImpl*>(GetWebUI())->OnMessageReceived(message)) {
-    return true;
+
+  if (render_view_host) {
+    RenderFrameHost* main_frame = render_view_host->GetMainFrame();
+    if (main_frame) {

[jam, 2016/12/08 17:43:53]

nit: are you sure you need this check?

[yzshen1, 2016/12/08 17:46:19]

Yes, there are cases where render_view_host->GetMainFrame() returns null. I
didn't look deeper to see whether those are expected though. Do you think it is
a bug?

Thanks! 

+      WebUIImpl* web_ui =
+          static_cast<RenderFrameHostImpl*>(main_frame)->web_ui();
+      if (web_ui && web_ui->OnMessageReceived(message))
+        return true;
+    }
   }
 
   if (render_frame_host) {