Make chrome/browser/extensions use base::Clock instead of MockTimeProvider

base/test/simple_test_tick_clock.h

 // Copyright (c) 2012 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 BASE_SIMPLE_TEST_TICK_CLOCK_H_
 #define BASE_SIMPLE_TEST_TICK_CLOCK_H_
 
 #include "base/compiler_specific.h"
 #include "base/synchronization/lock.h"
 #include "base/time.h"
 #include "base/time/tick_clock.h"
 
 namespace base {
 
 // SimpleTestTickClock is a TickClock implementation that gives
-// control over the returned TimeTicks objects.  All methods can be
+// control over the returned TimeTicks objects.  All methods may be
 // called from any thread.
 class SimpleTestTickClock : public TickClock {
  public:
   // Starts off with a clock set to TimeTicks().
   SimpleTestTickClock();
   virtual ~SimpleTestTickClock();
 
   virtual TimeTicks NowTicks() OVERRIDE;
 
-  // Sets the current time forward by |delta|.  Safe to call from any
-  // thread.
+  // Advances the clock by |delta|, which must not be negative.
   void Advance(TimeDelta delta);
 
  private:
   // Protects |now_ticks_|.
   Lock lock_;
 
   TimeTicks now_ticks_;
 };
 
 }  // namespace base
 
 #endif  // BASE_SIMPLE_TEST_TICK_CLOCK_H_