[cc] Remove remaining_frames from BeginFrameAck.

cc/output/begin_frame_args.h

Index: cc/output/begin_frame_args.h
diff --git a/cc/output/begin_frame_args.h b/cc/output/begin_frame_args.h
index 41b156ad708d33692eed652b8c58a4466df3b4f7..d4ced74a32c9bac8c462864f32e6b815151b8962 100644
--- a/cc/output/begin_frame_args.h
+++ b/cc/output/begin_frame_args.h
@@ -122,7 +122,6 @@ struct CC_EXPORT BeginFrameAck {
   BeginFrameAck(uint32_t source_id,
                 uint64_t sequence_number,
                 uint64_t latest_confirmed_sequence_number,
-                uint32_t remaining_frames,
                 bool has_damage);
 
   // Creates a BeginFrameAck for a manual BeginFrame. Used when clients produce
@@ -168,10 +167,6 @@ struct CC_EXPORT BeginFrameAck {
   // BeginFrame from the old source is still in flight.
   uint32_t source_id;  // |source_id| after above fields for packing.
 
-  // Number of BeginFrames queued at the observer at time of acknowledgment.
-  // TODO(eseckler): Remove this field and replace with ack-tracking if needed.
-  uint32_t remaining_frames;
-
   // |true| if the observer has produced damage (e.g. sent a CompositorFrame or
   // damaged a surface) as part of responding to the BeginFrame.
   bool has_damage;