[cc] Remove BeginFrameAck from BFS::DidFinishFrame and update tests.

cc/scheduler/scheduler.cc

Index: cc/scheduler/scheduler.cc
diff --git a/cc/scheduler/scheduler.cc b/cc/scheduler/scheduler.cc
index e3fdef521d81652995c01a4242a52f15d31ded82..d1d0bdda52636b026b2bbe44c2b4af9f5144e671 100644
--- a/cc/scheduler/scheduler.cc
+++ b/cc/scheduler/scheduler.cc
@@ -443,27 +443,26 @@ void Scheduler::FinishImplFrame() {
 
 void Scheduler::SendBeginFrameAck(const BeginFrameArgs& args,
                                   BeginFrameResult result) {
-  if (!begin_frame_source_)
-    return;
-
-  uint64_t latest_confirmed_sequence_number =
-      BeginFrameArgs::kInvalidFrameNumber;
-  if (args.source_id == state_machine_.begin_frame_source_id()) {
-    latest_confirmed_sequence_number =
-        state_machine_
-            .last_begin_frame_sequence_number_compositor_frame_was_fresh();
-  }
-
   bool did_submit = false;
-  if (result == kBeginFrameFinished) {
+  if (result == kBeginFrameFinished)
     did_submit = state_machine_.did_submit_in_last_frame();
+
+  if (!did_submit) {
+    uint64_t latest_confirmed_sequence_number =
+        BeginFrameArgs::kInvalidFrameNumber;
+    if (args.source_id == state_machine_.begin_frame_source_id()) {
+      latest_confirmed_sequence_number =
+          state_machine_
+              .last_begin_frame_sequence_number_compositor_frame_was_fresh();
+    }
+
+    client_->DidNotProduceFrame(
+        BeginFrameAck(args.source_id, args.sequence_number,
+                      latest_confirmed_sequence_number, did_submit));
   }
 
-  BeginFrameAck ack(args.source_id, args.sequence_number,
-                    latest_confirmed_sequence_number, did_submit);
-  begin_frame_source_->DidFinishFrame(this, ack);
-  if (!did_submit)
-    client_->DidNotProduceFrame(ack);
+  if (begin_frame_source_)
+    begin_frame_source_->DidFinishFrame(this);

[sunnyps, 2017/05/24 02:38:25]

nit: Move this to FinishImplFrame because that's the only place where this is
relevant.

[Eric Seckler, 2017/05/24 09:00:40]

Is this true? I think we also want to ack to the (BackToBack)BeginFrameSource if
we skip a BeginFrame during OnBeginFrameDerivedImpl() without triggering a
BeginImplFrame.

I'll leave this as-is for now.

[sunnyps, 2017/05/25 20:20:27]

We skip begin frames in two cases:
1. not expecting begin frames
2. impl latency recovery which is disabled for !throttled BFS (back to back)

We don't need to call DidFinishFrame in both cases.

[Eric Seckler, 2017/05/26 08:55:31]

Still leaving as-is as discussed offline (the BFS interface doesn't really
clarify that this only needs to be called if BFS may be BackToBack).

 }
 
 // BeginImplFrame starts a compositor frame that will wait up until a deadline