[cc] Calculate the correct latest_confirmed_sequence_number in cc::Scheduler.

cc/scheduler/scheduler.cc

Index: cc/scheduler/scheduler.cc
diff --git a/cc/scheduler/scheduler.cc b/cc/scheduler/scheduler.cc
index d8f9440227d4b858b6190b63fe3baab87aa513c9..b903cbad41935d7ca3528998d44089d403f5367a 100644
--- a/cc/scheduler/scheduler.cc
+++ b/cc/scheduler/scheduler.cc
@@ -322,9 +322,10 @@ 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) {
-    // TODO(eseckler): Determine and set correct |ack.latest_confirmed_frame|.
-    BeginFrameAck ack(adjusted_args.source_id, adjusted_args.sequence_number,
-                      adjusted_args.sequence_number, 0, false);
+    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;
   }
@@ -335,9 +336,10 @@ void Scheduler::BeginImplFrameWithDeadline(const BeginFrameArgs& args) {
     OnBeginImplFrameDeadline();
     // We may not need begin frames any longer.
     if (!observing_begin_frame_source_) {
-      // TODO(eseckler): Determine and set correct |ack.latest_confirmed_frame|.
-      BeginFrameAck ack(adjusted_args.source_id, adjusted_args.sequence_number,
-                        adjusted_args.sequence_number, 0, false);
+      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;
     }
@@ -398,9 +400,10 @@ void Scheduler::BeginImplFrameWithDeadline(const BeginFrameArgs& args) {
     TRACE_EVENT_INSTANT0("cc", "SkipBeginImplFrameToReduceLatency",
                          TRACE_EVENT_SCOPE_THREAD);
     if (begin_frame_source_) {
-      // TODO(eseckler): Determine and set correct |ack.latest_confirmed_frame|.
-      BeginFrameAck ack(adjusted_args.source_id, adjusted_args.sequence_number,
-                        adjusted_args.sequence_number, 0, false);
+      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;
@@ -431,11 +434,11 @@ void Scheduler::FinishImplFrame() {
 
   client_->DidFinishImplFrame();
   if (begin_frame_source_) {
-    // TODO(eseckler): Determine and set correct |ack.latest_confirmed_frame|.
-    BeginFrameAck ack(begin_main_frame_args_.source_id,
-                      begin_main_frame_args_.sequence_number,
-                      begin_main_frame_args_.sequence_number, 0,
-                      state_machine_.did_submit_in_last_frame());
+    BeginFrameAck ack(
+        begin_main_frame_args_.source_id,

[brianderson, 2017/01/13 19:13:49]

The begin_main_frame_args_.source_id at this point might not correspond to the
same source_id that created last_frame_number_compositor_frame_was_fresh. I
think you'll need to track multiple source_ids through the pipeline just like
you did with the last_frame_number*s.

[Sami, 2017/01/16 10:41:02]

I think this is okay, because when the source_id changes we reset everything to
be fresh up to that point, which is effectively doing the same thing as would
checking source_id here. However Eric noticed we're not always telling the state
machine when the source_id might change, so he's gonna fix that still. FWIW we
also decided to reset to everything to kInvalidSequenceNumber to make it more
obvious that there was a discontinuity.

[Eric Seckler, 2017/01/16 14:33:01]

What Sami said. :) Regarding telling the state machine about source_id changes,
I'm now telling it about every BeginFrame received by the Scheduler to update
the sequence numbers even in cases where we skip a BeginImplFrame().

[Eric Seckler, 2017/01/17 18:01:24]

Badum.. I'm just realizing that this is broken since
BeginImplFrameWithDeadline() may trigger the previous BeginFrame's deadline.
I'll have to think about a different solution for this... :)

+        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();
@@ -451,7 +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());