PlzNavigate: fix timing issue in app window creation

content/test/web_contents_observer_sanity_checker.h

 // Copyright 2014 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_TEST_WEB_CONTENTS_OBSERVER_SANITY_CHECKER_H_
 #define CONTENT_TEST_WEB_CONTENTS_OBSERVER_SANITY_CHECKER_H_
 
 #include <set>
 #include <string>
 
@@ skipping 24 matching lines @@
   // WebContentsObserver implementation.
   void RenderFrameCreated(RenderFrameHost* render_frame_host) override;
   void RenderFrameDeleted(RenderFrameHost* render_frame_host) override;
   void RenderFrameForInterstitialPageCreated(
       RenderFrameHost* render_frame_host) override;
   void RenderFrameHostChanged(RenderFrameHost* old_host,
                               RenderFrameHost* new_host) override;
   void FrameDeleted(RenderFrameHost* render_frame_host) override;
   void DidStartNavigation(NavigationHandle* navigation_handle) override;
   void DidRedirectNavigation(NavigationHandle* navigation_handle) override;
+  void AboutToCommitNavigation(NavigationHandle* navigation_handle) override;
   void DidCommitNavigation(NavigationHandle* navigation_handle) override;
   void DidFinishNavigation(NavigationHandle* navigation_handle) override;
   void DidStartProvisionalLoadForFrame(RenderFrameHost* render_frame_host,
                                        const GURL& validated_url,
                                        bool is_error_page,
                                        bool is_iframe_srcdoc) override;
   void DidCommitProvisionalLoadForFrame(
       RenderFrameHost* render_frame_host,
       const GURL& url,
       ui::PageTransition transition_type) override;
@@ skipping 49 matching lines @@
   std::set<NavigationHandle*> ongoing_committed_navigations_;
 
   bool web_contents_destroyed_;
 
   DISALLOW_COPY_AND_ASSIGN(WebContentsObserverSanityChecker);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_TEST_WEB_CONTENTS_OBSERVER_SANITY_CHECKER_H_