cc: Introduce BeginFrame sequence numbers and acknowledgements.

cc/scheduler/scheduler.cc

Index: cc/scheduler/scheduler.cc
diff --git a/cc/scheduler/scheduler.cc b/cc/scheduler/scheduler.cc
index 14d5e69e6a0b6521be64398bb0755aca1ce5e559..8fdb97d3390de92d0e0e07beee07d78e99d46d76 100644
--- a/cc/scheduler/scheduler.cc
+++ b/cc/scheduler/scheduler.cc
@@ -322,7 +322,11 @@ void Scheduler::BeginImplFrameWithDeadline(const BeginFrameArgs& args) {
   // Discard missed begin frames if they are too late.
   if (adjusted_args.type == BeginFrameArgs::MISSED &&
       now > adjusted_args.deadline) {
-    begin_frame_source_->DidFinishFrame(this, 0);
+    BeginFrameAck ack(
+        adjusted_args.source_id, adjusted_args.sequence_number,
+        state_machine_.last_frame_number_compositor_frame_was_fresh(), 0,
+        false);
+    begin_frame_source_->DidFinishFrame(this, ack);
     return;
   }
 
@@ -332,7 +336,11 @@ void Scheduler::BeginImplFrameWithDeadline(const BeginFrameArgs& args) {
     OnBeginImplFrameDeadline();
     // We may not need begin frames any longer.
     if (!observing_begin_frame_source_) {
-      begin_frame_source_->DidFinishFrame(this, 0);
+      BeginFrameAck ack(
+          adjusted_args.source_id, adjusted_args.sequence_number,
+          state_machine_.last_frame_number_compositor_frame_was_fresh(), 0,
+          false);
+      begin_frame_source_->DidFinishFrame(this, ack);
       return;
     }
   }
@@ -391,8 +399,13 @@ void Scheduler::BeginImplFrameWithDeadline(const BeginFrameArgs& args) {
                                       can_activate_before_deadline)) {
     TRACE_EVENT_INSTANT0("cc", "SkipBeginImplFrameToReduceLatency",
                          TRACE_EVENT_SCOPE_THREAD);
-    if (begin_frame_source_)
-      begin_frame_source_->DidFinishFrame(this, 0);
+    if (begin_frame_source_) {
+      BeginFrameAck ack(
+          adjusted_args.source_id, adjusted_args.sequence_number,
+          state_machine_.last_frame_number_compositor_frame_was_fresh(), 0,
+          false);
+      begin_frame_source_->DidFinishFrame(this, ack);
+    }
     return;
   }
 
@@ -420,8 +433,14 @@ void Scheduler::FinishImplFrame() {
   ProcessScheduledActions();
 
   client_->DidFinishImplFrame();
-  if (begin_frame_source_)
-    begin_frame_source_->DidFinishFrame(this, 0);
+  if (begin_frame_source_) {
+    BeginFrameAck ack(
+        begin_main_frame_args_.source_id,
+        begin_main_frame_args_.sequence_number,
+        state_machine_.last_frame_number_compositor_frame_was_fresh(), 0,
+        state_machine_.did_submit_in_last_frame());
+    begin_frame_source_->DidFinishFrame(this, ack);
+  }
   begin_impl_frame_tracker_.Finish();
 }
 
@@ -435,7 +454,7 @@ void Scheduler::BeginImplFrame(const BeginFrameArgs& args) {
   DCHECK(state_machine_.HasInitializedCompositorFrameSink());
 
   begin_impl_frame_tracker_.Start(args);
-  state_machine_.OnBeginImplFrame();
+  state_machine_.OnBeginImplFrame(args.source_id, args.sequence_number);
   devtools_instrumentation::DidBeginFrame(layer_tree_host_id_);
   compositor_timing_history_->WillBeginImplFrame(
       state_machine_.NewActiveTreeLikely());
@@ -757,4 +776,16 @@ bool Scheduler::IsBeginMainFrameSentOrStarted() const {
               SchedulerStateMachine::BEGIN_MAIN_FRAME_STATE_STARTED);
 }
 
+uint64_t Scheduler::CurrentBeginFrameSourceId() {
+  return begin_main_frame_args_.source_id;
+}
+
+uint64_t Scheduler::CurrentBeginFrameNumber() {
+  return begin_main_frame_args_.sequence_number;
+}
+
+uint64_t Scheduler::LatestConfirmedFrameForActiveTree() {
+  return state_machine_.last_frame_number_active_tree_was_fresh();
+}
+
 }  // namespace cc