Add UMA histograms for data usage tab model

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 <stdint.h>
 
 #include <string>
 
 #include "base/containers/hash_tables.h"
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "base/observer_list_threadsafe.h"
 #include "base/threading/thread_checker.h"
+#include "base/time/time.h"
 #include "chrome/browser/android/data_usage/tab_data_use_entry.h"
 #include "components/data_usage/core/data_use.h"
 #include "url/gurl.h"
 
 namespace chrome {
 
 namespace android {
 
 class ExternalDataUseObserver;
 
@@ skipping 90 matching lines @@
   FRIEND_TEST_ALL_PREFIXES(DataUseTabModelTest, MultipleTabTracking);
   FRIEND_TEST_ALL_PREFIXES(DataUseTabModelTest, ObserverStartEndEvents);
   FRIEND_TEST_ALL_PREFIXES(DataUseTabModelTest, ObserverNotNotifiedAfterRemove);
   FRIEND_TEST_ALL_PREFIXES(DataUseTabModelTest,
                            MultipleObserverMultipleStartEndEvents);
   FRIEND_TEST_ALL_PREFIXES(DataUseTabModelTest, TabCloseEvent);
   FRIEND_TEST_ALL_PREFIXES(DataUseTabModelTest, TabCloseEventEndsTracking);
   FRIEND_TEST_ALL_PREFIXES(DataUseTabModelTest, OnTrackingLabelRemoved);
   FRIEND_TEST_ALL_PREFIXES(DataUseTabModelTest,
                            CompactTabEntriesWithinMaxLimit);
+  FRIEND_TEST_ALL_PREFIXES(DataUseTabModelTest,
+                           UnexpiredTabEntryRemovaltimeHistogram);
+  FRIEND_TEST_ALL_PREFIXES(DataUseTabModelTest,
+                           ExpiredInactiveTabEntryRemovaltimeHistogram);
+  FRIEND_TEST_ALL_PREFIXES(DataUseTabModelTest,
+                           ExpiredActiveTabEntryRemovaltimeHistogram);
 
   typedef base::hash_map<int32_t, TabDataUseEntry> TabEntryMap;
 
+  // Virtualized for unit test support.
+  virtual base::TimeTicks Now() const;
+
   // Notifies the observers that a data usage tracking session started for
   // |tab_id|.
   void NotifyObserversOfTrackingStarting(int32_t tab_id);
 
   // Notifies the observers that an active data usage tracking session ended for
   // |tab_id|.
   void NotifyObserversOfTrackingEnding(int32_t tab_id);
 
   // Initiates a new tracking session with the |label| for tab with id |tab_id|.
   void StartTrackingDataUse(int32_t tab_id, const std::string& label);
@@ skipping 28 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_