[cc] Remove remaining_frames from BeginFrameAck.

cc/output/begin_frame_args.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_OUTPUT_BEGIN_FRAME_ARGS_H_
 #define CC_OUTPUT_BEGIN_FRAME_ARGS_H_
 
 #include <stdint.h>
 #include <memory>
 
@@ skipping 104 matching lines @@
                  base::TimeDelta interval,
                  BeginFrameArgsType type);
 };
 
 // Sent by a BeginFrameObserver as acknowledgment of completing a BeginFrame.
 struct CC_EXPORT BeginFrameAck {
   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
   // a CompositorFrame without prior BeginFrame, e.g. for synchronous drawing.
   static BeginFrameAck CreateManualAckWithDamage();
 
   // Sequence number of the BeginFrame that is acknowledged.
   uint64_t sequence_number;
 
   // Sequence number of the latest BeginFrame that was positively acknowledged
@@ skipping 25 matching lines @@
   // observers according to above comment.
   uint64_t latest_confirmed_sequence_number;
 
   // Source identifier of the BeginFrame that is acknowledged. The
   // BeginFrameSource that receives the acknowledgment uses this to discard
   // BeginFrameAcks for BeginFrames sent by a different source. Such a situation
   // may occur when the BeginFrameSource of the observer changes while a
   // 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;
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_BEGIN_FRAME_ARGS_H_