Make ExternalDataUseReporter independent of other data use classes

chrome/browser/android/data_usage/data_use_tab_model.h

 // Copyright 2015 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 CHROME_BROWSER_ANDROID_DATA_USAGE_DATA_USE_TAB_MODEL_H_
 #define CHROME_BROWSER_ANDROID_DATA_USAGE_DATA_USE_TAB_MODEL_H_
 
 #include <stddef.h>
 
 #include <memory>
@@ skipping 133 matching lines @@
   // the TabDataUseObserver.
   virtual void OnTrackingLabelRemoved(const std::string& label);
 
   // Gets the tracking information for the tab with id |tab_id| at time
   // |timestamp|. |output_info| must not be null. If a tab tracking session is
   // found that was active at |timestamp|, returns true and
   // |output_tracking_info| is populated with its information. Otherwise,
   // returns false.
   virtual bool GetTrackingInfoForTabAtTime(
       SessionID::id_type tab_id,
-      base::TimeTicks timestamp,
+      const base::TimeTicks& timestamp,

[tbansal1, 2016/07/21 00:19:30]

Passing by value is preferable.
See https://cs.chromium.org/chromium/src/base/time/time.h?rcl=0&l=24

[Raj, 2016/07/21 04:09:16]

Done.

       TrackingInfo* output_tracking_info) const;
 
   // Returns true if the navigation event would end the tracking session for
   // |tab_id|. |transition| is the type of the UI event/transition. |url| is the
   // URL in the tab. |navigation_entry| which can be null corresponds to the
   // navigation entry of the current navigation in back-forward navigation
   // history.
   bool WouldNavigationEventEndTracking(
       SessionID::id_type tab_id,
       TransitionType transition,
@@ skipping 157 matching lines @@
   base::WeakPtrFactory<DataUseTabModel> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DataUseTabModel);
 };
 
 }  // namespace android
 
 }  // namespace chrome
 
 #endif  // CHROME_BROWSER_ANDROID_DATA_USAGE_DATA_USE_TAB_MODEL_H_