Make Callback::Reset() return a copy to support use-cases where Run() ends up modifying |*this|.

media/base/filters.h

Index: media/base/filters.h
diff --git a/media/base/filters.h b/media/base/filters.h
index 242af5cfeb6d8269fe1595cafdab276a4c5a6622..e101347aa86d1bccf3dc2e81c87405a9b78622e3 100644
--- a/media/base/filters.h
+++ b/media/base/filters.h
@@ -50,12 +50,6 @@ struct PipelineStatistics;
 // Used for completing asynchronous methods.
 typedef base::Callback<void(PipelineStatus)> FilterStatusCB;
 
-// These functions copy |*cb|, call Reset() on |*cb|, and then call Run()
-// on the copy.  This is used in the common case where you need to clear
-// a callback member variable before running the callback.
-MEDIA_EXPORT void ResetAndRunCB(FilterStatusCB* cb, PipelineStatus status);
-MEDIA_EXPORT void ResetAndRunCB(base::Closure* cb);
-
 class MEDIA_EXPORT Filter : public base::RefCountedThreadSafe<Filter> {
  public:
   Filter();