cc: Introduce BeginFrame sequence numbers and acknowledgements.

cc/output/compositor_frame_metadata.h

 // Copyright (c) 2012 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_COMPOSITOR_FRAME_METADATA_H_
 #define CC_OUTPUT_COMPOSITOR_FRAME_METADATA_H_
 
 #include <stdint.h>
 
 #include <vector>
@@ skipping 64 matching lines @@
 
   std::vector<ui::LatencyInfo> latency_info;
 
   // A set of SurfaceSequences that this frame satisfies (always in the same
   // namespace as the current Surface).
   std::vector<uint32_t> satisfies_sequences;
 
   // This is the set of Surfaces that are referenced by this frame.
   std::vector<SurfaceId> referenced_surfaces;
 
+  // Source identifier of the BeginFrame that this frame is in response to.
+  uint64_t begin_frame_source_id = 0;
+  // Sequence number of the BeginFrame that this frame is in response to.
+  uint64_t begin_frame_number = 0;
+  // Sequence number of the latest BeginFrame that is confirmed by this frame.
+  uint64_t latest_confirmed_frame = 0;
+
  private:
   CompositorFrameMetadata(const CompositorFrameMetadata& other);
   CompositorFrameMetadata operator=(const CompositorFrameMetadata&) = delete;
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_COMPOSITOR_FRAME_METADATA_H_