cc: Introduce BeginFrame sequence numbers and acknowledgements.

cc/scheduler/scheduler_state_machine.cc

Index: cc/scheduler/scheduler_state_machine.cc
diff --git a/cc/scheduler/scheduler_state_machine.cc b/cc/scheduler/scheduler_state_machine.cc
index 4a9a2e0991914bfea1843ceea75f23397ea56d63..b917e27f95989e7f00ee2cb7cedd39084140d00b 100644
--- a/cc/scheduler/scheduler_state_machine.cc
+++ b/cc/scheduler/scheduler_state_machine.cc
@@ -25,11 +25,15 @@ SchedulerStateMachine::SchedulerStateMachine(const SchedulerSettings& settings)
       begin_main_frame_state_(BEGIN_MAIN_FRAME_STATE_IDLE),
       forced_redraw_state_(FORCED_REDRAW_STATE_IDLE),
       commit_count_(0),
-      current_frame_number_(0),
-      last_frame_number_submit_performed_(-1),
-      last_frame_number_draw_performed_(-1),
-      last_frame_number_begin_main_frame_sent_(-1),
-      last_frame_number_invalidate_compositor_frame_sink_performed_(-1),
+      begin_frame_source_id_(0),
+      current_frame_number_(1),
+      last_frame_number_submit_performed_(0),
+      last_frame_number_draw_performed_(0),
+      last_frame_number_begin_main_frame_sent_(0),
+      last_frame_number_invalidate_compositor_frame_sink_performed_(0),
+      last_frame_number_pending_tree_was_fresh_(0),
+      last_frame_number_active_tree_was_fresh_(0),
+      last_frame_number_compositor_frame_was_fresh_(0),
       draw_funnel_(false),
       send_begin_main_frame_funnel_(true),
       invalidate_compositor_frame_sink_funnel_(false),
@@ -207,6 +211,7 @@ void SchedulerStateMachine::AsValueInto(
 
   state->BeginDictionary("minor_state");
   state->SetInteger("commit_count", commit_count_);
+  state->SetInteger("begin_frame_source_id", begin_frame_source_id_);
   state->SetInteger("current_frame_number", current_frame_number_);
   state->SetInteger("last_frame_number_submit_performed",
                     last_frame_number_submit_performed_);
@@ -214,6 +219,12 @@ void SchedulerStateMachine::AsValueInto(
                     last_frame_number_draw_performed_);
   state->SetInteger("last_frame_number_begin_main_frame_sent",
                     last_frame_number_begin_main_frame_sent_);
+  state->SetInteger("last_frame_number_pending_tree_was_fresh",
+                    last_frame_number_pending_tree_was_fresh_);
+  state->SetInteger("last_frame_number_active_tree_was_fresh",
+                    last_frame_number_active_tree_was_fresh_);
+  state->SetInteger("last_frame_number_compositor_frame_was_fresh",
+                    last_frame_number_compositor_frame_was_fresh_);
   state->SetBoolean("funnel: draw_funnel", draw_funnel_);
   state->SetBoolean("funnel: send_begin_main_frame_funnel",
                     send_begin_main_frame_funnel_);
@@ -589,10 +600,22 @@ void SchedulerStateMachine::WillCommit(bool commit_has_no_updates) {
   last_commit_had_no_updates_ = commit_has_no_updates;
   begin_main_frame_state_ = BEGIN_MAIN_FRAME_STATE_IDLE;
 
-  if (!commit_has_no_updates) {
-    // Pending tree only exists if commit had updates.
+  if (commit_has_no_updates) {
+    // Pending tree might still exist from prior commit.
+    if (has_pending_tree_) {
+      DCHECK(settings_.main_frame_before_activation_enabled);
+      last_frame_number_pending_tree_was_fresh_ =
+          last_frame_number_begin_main_frame_sent_;
+    } else {
+      last_frame_number_active_tree_was_fresh_ =
+          last_frame_number_begin_main_frame_sent_;
+    }
+  } else {
+    // We have a new pending tree.
     has_pending_tree_ = true;
     pending_tree_is_ready_for_activation_ = false;
+    last_frame_number_pending_tree_was_fresh_ =
+        last_frame_number_begin_main_frame_sent_;
     wait_for_ready_to_draw_ = settings_.commit_to_active_tree;
   }
 
@@ -824,9 +847,24 @@ bool SchedulerStateMachine::ProactiveBeginFrameWanted() const {
   return false;
 }
 
-void SchedulerStateMachine::OnBeginImplFrame() {
+void SchedulerStateMachine::OnBeginImplFrame(uint64_t source_id,
+                                             uint64_t sequence_number) {
+  if (source_id != begin_frame_source_id_) {
+    begin_frame_source_id_ = source_id;
+    current_frame_number_ = sequence_number;
+
+    // Consider us up to date up to the previous BeginFrame.
+    last_frame_number_active_tree_was_fresh_ = current_frame_number_ - 1;
+    last_frame_number_pending_tree_was_fresh_ =
+        last_frame_number_active_tree_was_fresh_;
+    last_frame_number_compositor_frame_was_fresh_ =
+        last_frame_number_active_tree_was_fresh_;
+  }
+
+  DCHECK_GE(sequence_number, current_frame_number_);
+
   begin_impl_frame_state_ = BEGIN_IMPL_FRAME_STATE_INSIDE_BEGIN_FRAME;
-  current_frame_number_++;
+  current_frame_number_ = sequence_number;
 
   last_commit_had_no_updates_ = false;
   did_draw_in_last_frame_ = false;
@@ -840,6 +878,18 @@ void SchedulerStateMachine::OnBeginImplFrame() {
   // "Drain" the PrepareTiles funnel.
   if (prepare_tiles_funnel_ > 0)
     prepare_tiles_funnel_--;
+
+  // Update frame numbers for freshness if no updates are requested.
+  if (!needs_begin_main_frame_) {
+    if (has_pending_tree_) {
+      last_frame_number_pending_tree_was_fresh_ = current_frame_number_;
+    } else {
+      last_frame_number_active_tree_was_fresh_ = current_frame_number_;
+
+      if (!needs_redraw_)
+        last_frame_number_compositor_frame_was_fresh_ = current_frame_number_;
+    }
+  }
 }
 
 void SchedulerStateMachine::OnBeginImplFrameDeadline() {
@@ -985,6 +1035,8 @@ void SchedulerStateMachine::DidSubmitCompositorFrame() {
 
   did_submit_in_last_frame_ = true;
   last_frame_number_submit_performed_ = current_frame_number_;
+  last_frame_number_compositor_frame_was_fresh_ =
+      last_frame_number_active_tree_was_fresh_;
 }
 
 void SchedulerStateMachine::DidReceiveCompositorFrameAck() {