Update comments for rename of ScalingObserverInterface.

Was renamed to AdaptationObserverInterface in cl
https://codereview.webrtc.org/2652893015/.

Bug: webrtc:4172
Change-Id: Ie2194a1fd5fe985913716963292af701006f18dd
Reviewed-on: https://webrtc-review.googlesource.com/6420
Reviewed-by: Erik Språng <sprang@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20155}
diff --git a/video/video_stream_encoder.h b/video/video_stream_encoder.h
index f90a07d..3cc46a3 100644
--- a/video/video_stream_encoder.h
+++ b/video/video_stream_encoder.h
@@ -126,7 +126,7 @@
   // be called on |encoder_queue_|.
   rtc::TaskQueue* encoder_queue() { return &encoder_queue_; }
 
-  // webrtc::ScalingObserverInterface implementation.
+  // AdaptationObserverInterface implementation.
   // These methods are protected for easier testing.
   void AdaptUp(AdaptReason reason) override;
   void AdaptDown(AdaptReason reason) override;