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

components/app_modal/javascript_dialog_manager.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_DIALOG_MANAGER_H_
 #define COMPONENTS_APP_MODAL_JAVASCRIPT_DIALOG_MANAGER_H_
 
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/singleton.h"
+#include "base/time/time.h"
 #include "components/app_modal/javascript_app_modal_dialog.h"
 #include "content/public/browser/javascript_dialog_manager.h"
 
 namespace app_modal {
 
 class JavaScriptDialogExtensionsClient;
 class JavaScriptNativeDialogFactory;
 
 class JavaScriptDialogManager : public content::JavaScriptDialogManager {
  public:
@@ skipping 52 matching lines @@
                       bool success,
                       const base::string16& user_input);
 
   // Mapping between the WebContents and their extra data. The key
   // is a void* because the pointer is just a cookie and is never dereferenced.
   JavaScriptAppModalDialog::ExtraDataMap javascript_dialog_extra_data_;
 
   scoped_ptr<JavaScriptNativeDialogFactory> native_dialog_factory_;
   scoped_ptr<JavaScriptDialogExtensionsClient> extensions_client_;
 
+  // Record a single create and close timestamp to track the time between
+  // dialogs. (Since Javascript dialogs are modal, this is even accurate!)
+  base::TimeTicks last_close_time_;
+  base::TimeTicks last_creation_time_;
+
   DISALLOW_COPY_AND_ASSIGN(JavaScriptDialogManager);
 };
 
 }  // namespace app_modal
 
 #endif  // COMPONENTS_APP_MODAL_JAVASCRIPT_DIALOG_MANAGER_H_