[cc] Add and use BeginFrameAck for DidFinishFrame.

cc/output/begin_frame_args.cc

Index: cc/output/begin_frame_args.cc
diff --git a/cc/output/begin_frame_args.cc b/cc/output/begin_frame_args.cc
index f7a35ff3540e7e741607e5a0a912a758fdd4f254..d3000d25bfa25ca4493baf2a9942fbbac8ec84c8 100644
--- a/cc/output/begin_frame_args.cc
+++ b/cc/output/begin_frame_args.cc
@@ -108,4 +108,24 @@ base::TimeDelta BeginFrameArgs::DefaultInterval() {
   return base::TimeDelta::FromMicroseconds(16666);
 }
 
+BeginFrameAck::BeginFrameAck()
+    : source_id(0),
+      sequence_number(BeginFrameArgs::kInvalidFrameNumber),
+      latest_confirmed_frame(BeginFrameArgs::kInvalidFrameNumber),
+      remaining_frames(0),
+      has_damage(false) {}
+
+BeginFrameAck::BeginFrameAck(uint64_t source_id,
+                             uint64_t sequence_number,
+                             uint64_t latest_confirmed_frame,
+                             uint32_t remaining_frames,
+                             bool has_damage)
+    : source_id(source_id),
+      sequence_number(sequence_number),
+      latest_confirmed_frame(latest_confirmed_frame),
+      remaining_frames(remaining_frames),
+      has_damage(has_damage) {
+  DCHECK_LT(BeginFrameArgs::kInvalidFrameNumber, sequence_number);
+}
+
 }  // namespace cc