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

media/filters/video_renderer_base.cc

Index: media/filters/video_renderer_base.cc
diff --git a/media/filters/video_renderer_base.cc b/media/filters/video_renderer_base.cc
index 47db2ecf120573d41d69a34b30ef41bf65ef394d..08a8271621beaa31e14d0954b0d797eb82ea0654 100644
--- a/media/filters/video_renderer_base.cc
+++ b/media/filters/video_renderer_base.cc
@@ -4,6 +4,7 @@
 
 #include "base/bind.h"
 #include "base/callback.h"
+#include "base/callback_helpers.h"
 #include "base/threading/platform_thread.h"
 #include "media/base/buffers.h"
 #include "media/base/filter_host.h"
@@ -372,7 +373,7 @@ void VideoRendererBase::FrameReady(scoped_refptr<VideoFrame> frame) {
     // A new seek will be requested after this one completes so there is no
     // point trying to collect more frames.
     state_ = kPrerolled;
-    ResetAndRunCB(&seek_cb_, PIPELINE_OK);
+    base::ResetAndReturn(&seek_cb_).Run(PIPELINE_OK);
     return;
   }
 
@@ -431,7 +432,7 @@ void VideoRendererBase::FrameReady(scoped_refptr<VideoFrame> frame) {
 
     // ...and we're done seeking!
     DCHECK(!seek_cb_.is_null());
-    ResetAndRunCB(&seek_cb_, PIPELINE_OK);
+    base::ResetAndReturn(&seek_cb_).Run(PIPELINE_OK);
 
     base::AutoUnlock ul(lock_);
     paint_cb_.Run();