[cc] Add and use BeginFrameAck for DidFinishFrame.

cc/ipc/begin_frame_args_struct_traits.h

 // Copyright 2016 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_IPC_BEGIN_FRAME_ARGS_STRUCT_TRAITS_H_
 #define CC_IPC_BEGIN_FRAME_ARGS_STRUCT_TRAITS_H_
 
 #include "cc/ipc/begin_frame_args.mojom-shared.h"
 #include "cc/output/begin_frame_args.h"
 
@@ skipping 38 matching lines @@
     }
     out->source_id = data.source_id();
     out->sequence_number = data.sequence_number();
     out->type =
         static_cast<cc::BeginFrameArgs::BeginFrameArgsType>(data.type());
     out->on_critical_path = data.on_critical_path();
     return true;
   }
 };
 
+template <>
+struct StructTraits<cc::mojom::BeginFrameAckDataView, cc::BeginFrameAck> {
+  static uint64_t sequence_number(const cc::BeginFrameAck& ack) {
+    return ack.sequence_number;
+  }
+
+  static uint64_t latest_confirmed_sequence_number(
+      const cc::BeginFrameAck& ack) {
+    return ack.latest_confirmed_sequence_number;
+  }
+
+  static uint32_t source_id(const cc::BeginFrameAck& ack) {
+    return ack.source_id;
+  }
+
+  static uint32_t remaining_frames(const cc::BeginFrameAck& ack) {
+    return ack.remaining_frames;
+  }
+
+  static bool has_damage(const cc::BeginFrameAck& ack) {
+    return ack.has_damage;
+  }
+
+  static bool Read(cc::mojom::BeginFrameAckDataView data,
+                   cc::BeginFrameAck* out) {

[dcheng, 2017/01/05 06:49:54]

Nit: Read() methods should generally out-of-lined, can we do that here?

[Eric Seckler, 2017/01/06 16:08:51]

will do when we add it back in a later CL :)

+    out->source_id = data.source_id();
+    out->sequence_number = data.sequence_number();
+    out->latest_confirmed_sequence_number =
+        data.latest_confirmed_sequence_number();
+    out->remaining_frames = data.remaining_frames();
+    out->has_damage = data.has_damage();
+    return true;
+  }
+};
+
 }  // namespace mojo
 
 #endif  // CC_IPC_BEGIN_FRAME_ARGS_STRUCT_TRAITS_H_