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

media/filters/audio_renderer_base.cc

Index: media/filters/audio_renderer_base.cc
diff --git a/media/filters/audio_renderer_base.cc b/media/filters/audio_renderer_base.cc
index d04926f126f656fe70762a3ad7b64b2e43fbfc1f..f267eb953c6574b5974732e500cba4f0a354ac93 100644
--- a/media/filters/audio_renderer_base.cc
+++ b/media/filters/audio_renderer_base.cc
@@ -176,7 +176,7 @@ void AudioRendererBase::DecodedAudioReady(scoped_refptr<Buffer> buffer) {
       if (buffer && !buffer->IsEndOfStream())
         algorithm_->EnqueueBuffer(buffer);
       DCHECK(!pending_read_);
-      ResetAndRunCB(&pause_cb_);
+      pause_cb_.ResetAndRun();
       return;
     case kSeeking:
       if (IsBeforeSeekTime(buffer)) {
@@ -189,7 +189,7 @@ void AudioRendererBase::DecodedAudioReady(scoped_refptr<Buffer> buffer) {
           return;
       }
       state_ = kPaused;
-      ResetAndRunCB(&seek_cb_, PIPELINE_OK);
+      seek_cb_.ResetAndRun(PIPELINE_OK);
       return;
     case kPlaying:
     case kUnderflow: