Revert of base: Fix/add header #ifndef guards.

base/time/default_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_TIME_DEFAULT_CLOCK_H_
-#define BASE_TIME_DEFAULT_CLOCK_H_
+#ifndef BASE_DEFAULT_CLOCK_H_
+#define BASE_DEFAULT_CLOCK_H_
 
 #include "base/base_export.h"
 #include "base/compiler_specific.h"
 #include "base/time/clock.h"
 
 namespace base {
 
 // DefaultClock is a Clock implementation that uses Time::Now().
 class BASE_EXPORT DefaultClock : public Clock {
  public:
   ~DefaultClock() override;
 
   // Simply returns Time::Now().
   Time Now() override;
 };
 
 }  // namespace base
 
-#endif  // BASE_TIME_DEFAULT_CLOCK_H_
+#endif  // BASE_DEFAULT_CLOCK_H_