Revert r95841 due to failing media_unittests on linux_shared bot.

media/base/clock.h

Index: media/base/clock.h
===================================================================
--- media/base/clock.h	(revision 95843)
+++ media/base/clock.h	(working copy)
@@ -8,7 +8,6 @@
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/time.h"
-#include "media/base/media_export.h"
 
 namespace media {
 
@@ -25,7 +24,7 @@
 // TODO(scherkus): Clock will some day be responsible for executing callbacks
 // given a media time.  This will be used primarily by video renderers.  For now
 // we'll keep using a poll-and-sleep solution.
-class MEDIA_EXPORT Clock {
+class Clock {
  public:
   // Type for a static function pointer that acts as a time source.
   typedef base::Time(TimeProvider)();