Add UMA histograms for data usage tab model

chrome/browser/android/data_usage/tab_data_use_entry.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_TAB_DATA_USE_ENTRY_H_
 #define CHROME_BROWSER_ANDROID_DATA_USAGE_TAB_DATA_USE_ENTRY_H_
 
 #include <deque>
 #include <string>
 
@@ skipping 70 matching lines @@
   // time will be null if no tracking session was ever started or ended.
   const base::TimeTicks GetLatestStartOrEndTime() const;
 
  private:
   friend class TabDataUseEntryTest;
   friend class MockTabDataUseEntryTest;
   FRIEND_TEST_ALL_PREFIXES(TabDataUseEntryTest, SingleTabSessionCloseEvent);
   FRIEND_TEST_ALL_PREFIXES(TabDataUseEntryTest, MultipleTabSessionCloseEvent);
   FRIEND_TEST_ALL_PREFIXES(TabDataUseEntryTest, EndTrackingWithLabel);
   FRIEND_TEST_ALL_PREFIXES(DataUseTabModelTest, TabCloseEvent);
+  FRIEND_TEST_ALL_PREFIXES(DataUseTabModelTest,
+                           ExpiredInactiveTabEntryRemovaltimeHistogram);
+  FRIEND_TEST_ALL_PREFIXES(DataUseTabModelTest,
+                           ExpiredActiveTabEntryRemovaltimeHistogram);
   FRIEND_TEST_ALL_PREFIXES(MockTabDataUseEntryTest, CompactTabSessionHistory);
+  FRIEND_TEST_ALL_PREFIXES(MockTabDataUseEntryTest,
+                           OldInactiveSessionRemovaltimeHistogram);
 
   typedef std::deque<TabDataUseTrackingSession> TabSessions;
 
   // Virtualized for unit test support.
   virtual base::TimeTicks Now() const;
 
   // Compacts the history of tracking sessions by removing oldest sessions to
   // keep the size of |sessions_| within |kMaxSessionsPerTab| entries.
   void CompactSessionHistory();
 
@@ skipping 13 matching lines @@
   // respectively.
   const base::TimeDelta closed_tab_expiration_duration_;
   const base::TimeDelta open_tab_expiration_duration_;
 };
 
 }  // namespace android
 
 }  // namespace chrome
 
 #endif  // CHROME_BROWSER_ANDROID_DATA_USAGE_TAB_DATA_USE_ENTRY_H_