Change base::TickClock to a ref counted class.

content/browser/media/audio_stream_monitor.h

Index: content/browser/media/audio_stream_monitor.h
diff --git a/content/browser/media/audio_stream_monitor.h b/content/browser/media/audio_stream_monitor.h
index d1a32d5f857b05925f884ef64d834e673c8c5f29..149dd3e2371a8942b01685e5c15fa970ef9b18d6 100644
--- a/content/browser/media/audio_stream_monitor.h
+++ b/content/browser/media/audio_stream_monitor.h
@@ -11,6 +11,7 @@
 #include "base/callback_forward.h"
 #include "base/threading/thread_checker.h"
 #include "base/time/default_tick_clock.h"
+#include "base/time/tick_clock.h"
 #include "base/time/time.h"
 #include "base/timer/timer.h"
 #include "build/build_config.h"
@@ -112,15 +113,17 @@ class CONTENT_EXPORT AudioStreamMonitor {
   // on, |off_timer_| is started to re-invoke this method in the future.
   void MaybeToggle();
 
+  void set_clock_for_testing(const scoped_refptr<base::TickClock>& clock) {
+    clock_ = clock;
+  }
+
   // The WebContents instance instance to receive indicator toggle
   // notifications.  This pointer should be valid for the lifetime of
   // AudioStreamMonitor.
   WebContents* const web_contents_;
 
-  // Note: |clock_| is always |&default_tick_clock_|, except during unit
-  // testing.
-  base::DefaultTickClock default_tick_clock_;
-  base::TickClock* const clock_;
+  // Note: |clock_| is always a DefaultTickClock(), except during unit testing.
+  scoped_refptr<base::TickClock> clock_;
 
   // Confirms single-threaded access in debug builds.
   base::ThreadChecker thread_checker_;