Make ExternalDataUseReporter independent of other data use classes

chrome/browser/android/data_usage/data_use_tab_model.cc

 // 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.
 
 #include "chrome/browser/android/data_usage/data_use_tab_model.h"
 
 #include <stdint.h>
 
 #include "base/bind.h"
 #include "base/metrics/histogram_macros.h"
@@ skipping 204 matching lines @@
   tab_entry.OnTabCloseEvent();
 }
 
 void DataUseTabModel::OnTrackingLabelRemoved(const std::string& label) {
   for (auto& tab_entry : active_tabs_)
     tab_entry.second.EndTrackingWithLabel(label);
 }
 
 bool DataUseTabModel::GetTrackingInfoForTabAtTime(
     SessionID::id_type tab_id,
-    base::TimeTicks timestamp,
+    const base::TimeTicks& timestamp,
     TrackingInfo* output_tracking_info) const {
   DCHECK(thread_checker_.CalledOnValidThread());
 
   output_tracking_info->label = "";
 
   // Data use that cannot be attributed to a tab will not be labeled.
   if (!IsValidTabID(tab_id))
     return false;
 
   TabEntryMap::const_iterator tab_entry_iterator = active_tabs_.find(tab_id);
@@ skipping 278 matching lines @@
         NowTicks() -
             oldest_tab_entry_iterator->second.GetLatestStartOrEndTime(),
         base::TimeDelta::FromMinutes(1), base::TimeDelta::FromHours(1), 50);
     active_tabs_.erase(oldest_tab_entry_iterator);
   }
 }
 
 }  // namespace android
 
 }  // namespace chrome