[ObjC ARC] Converts ios/chrome/browser/metrics:metrics_internal to ARC.

ios/chrome/browser/metrics/tab_usage_recorder.h

 // Copyright 2013 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 IOS_CHROME_BROWSER_METRICS_TAB_USAGE_RECORDER_H_
 #define IOS_CHROME_BROWSER_METRICS_TAB_USAGE_RECORDER_H_
 
 #import <Foundation/Foundation.h>
 #include <deque>
 #include <map>
@@ skipping 173 matching lines @@
   void RecordRestoreStartTime();
 
   // Clears deleted tabs from |evicted_tabs_|.
   void ClearDeletedTabs();
 
   // Number of page loads since the last evicted tab was seen.
   unsigned int page_loads_;
 
   // Keep track of the current tab, but only if it has been evicted.
   // This is kept as a pointer value only - it should never be dereferenced.
-  void* evicted_tab_;
+  __unsafe_unretained Tab* evicted_tab_;
 
   // State of |evicted_tab_| at the time it became the current tab.
   TabStateWhenSelected evicted_tab_state_;
 
   // Keep track of the tab last selected when this tab model was switched
   // away from to another mode (e.g. to incognito).
   // Kept as a pointer value only - it should never be dereferenced.
-  void* mode_switch_tab_;
+  __unsafe_unretained Tab* mode_switch_tab_;
 
   // Keep track of a tab that was created to be immediately selected.  It should
   // not contribute to the "StatusWhenSwitchedBackToForeground" metric.
-  void* tab_created_selected_;
+  __unsafe_unretained Tab* tab_created_selected_;
 
   // Keep track of when the evicted tab starts to reload, so that the total
   // time it takes to reload can be recorded.
   base::TimeTicks evicted_tab_reload_start_time_;
 
   // Keep track of the tabs that have a known eviction cause.
   std::map<base::WeakNSObject<Tab>, TabStateWhenSelected> evicted_tabs_;
 
   // Reference to TabUsageRecorderDelegate which provides access to the count of
   // live tabs monitored by this recorder.
   base::WeakNSProtocol<id<TabUsageRecorderDelegate>> recorder_delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(TabUsageRecorder);
 };
 
 #endif  // IOS_CHROME_BROWSER_METRICS_TAB_USAGE_RECORDER_H_