Add UMA histograms to track very brief or frequent tabs and JS dialogs.

components/app_modal/javascript_app_modal_dialog.h

 // Copyright (c) 2012 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 COMPONENTS_APP_MODAL_JAVASCRIPT_APP_MODAL_DIALOG_H_
 #define COMPONENTS_APP_MODAL_JAVASCRIPT_APP_MODAL_DIALOG_H_
 
 #include <map>
 #include <string>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
+#include "base/time/time.h"
 #include "components/app_modal/app_modal_dialog.h"
 #include "content/public/browser/javascript_dialog_manager.h"
 
 namespace app_modal {
 
 // Extra data for JavaScript dialogs to add Chrome-only features.
 class ChromeJavaScriptDialogExtraData {
  public:
   ChromeJavaScriptDialogExtraData();
 
@@ skipping 72 matching lines @@
   bool is_before_unload_dialog_;
   bool is_reload_;
 
   content::JavaScriptDialogManager::DialogClosedCallback callback_;
 
   // Used only for testing. Specifies alternative prompt text that should be
   // used when notifying the delegate, if |use_override_prompt_text_| is true.
   base::string16 override_prompt_text_;
   bool use_override_prompt_text_;
 
+  base::TimeTicks creation_time_;
+
   DISALLOW_COPY_AND_ASSIGN(JavaScriptAppModalDialog);
 };
 
 }  // namespace app_modal
 
 #endif  // COMPONENTS_APP_MODAL_JAVASCRIPT_APP_MODAL_DIALOG_H_