Add UMA histograms for data usage tab model

chrome/browser/android/data_usage/data_use_tab_model.h

Index: chrome/browser/android/data_usage/data_use_tab_model.h
diff --git a/chrome/browser/android/data_usage/data_use_tab_model.h b/chrome/browser/android/data_usage/data_use_tab_model.h
index 43a07bdb110c5a8ac329cb20af38617e10afe9e3..4422874385f01c7e8e6f83a80cf6261618e85b3e 100644
--- a/chrome/browser/android/data_usage/data_use_tab_model.h
+++ b/chrome/browser/android/data_usage/data_use_tab_model.h
@@ -16,6 +16,7 @@
 #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"
@@ -77,7 +78,7 @@ class DataUseTabModel {
   DataUseTabModel(const ExternalDataUseObserver* data_use_observer,
                   scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner);
 
-  ~DataUseTabModel();
+  virtual ~DataUseTabModel();
 
   base::WeakPtr<DataUseTabModel> GetWeakPtr();
 
@@ -110,19 +111,22 @@ class DataUseTabModel {
  private:
   friend class DataUseTabModelTest;
   friend class MockTabDataUseEntryTest;
-  FRIEND_TEST_ALL_PREFIXES(DataUseTabModelTest, SingleTabTracking);
-  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,
                            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;
+
   // Returns the maximum number of tab entries to maintain session information
   // about.
   static size_t GetMaxTabEntriesForTests();