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 66 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(DataUseTabModelTest, TabCloseEvent);
   FRIEND_TEST_ALL_PREFIXES(MockTabDataUseEntryTest, CompactTabSessionHistory);
+  FRIEND_TEST_ALL_PREFIXES(MockTabDataUseEntryTest,
+                           OldInactiveSessionRemovaltimeHistogram);
+  FRIEND_TEST_ALL_PREFIXES(MockDataUseTabModelTest,
+                           ExpiredInactiveTabEntryRemovaltimeHistogram);
+  FRIEND_TEST_ALL_PREFIXES(MockDataUseTabModelTest,
+                           ExpiredActiveTabEntryRemovaltimeHistogram);
 
   typedef std::deque<TabDataUseTrackingSession> TabSessions;
 
   // Returns the maximum number of tracking sessions to maintain per tab, for
   // testing purposes.
   static size_t GetMaxSessionsPerTabForTests();
 
   // Returns the expiration duration in seconds for a closed tab entry and an
   // open tab entry respectively, for testing purposes.
   static unsigned int GetClosedTabExpirationDurationSecondsForTests();
@@ skipping 14 matching lines @@
   // Indicates the time the tab was closed. |tab_close_time_| will be null if
   // the tab is still open.
   base::TimeTicks tab_close_time_;
 };
 
 }  // namespace android
 
 }  // namespace chrome
 
 #endif  // CHROME_BROWSER_ANDROID_DATA_USAGE_TAB_DATA_USE_ENTRY_H_