[cc] Set BeginFrame sequence numbers on CompositorFrames from Scheduler.

cc/scheduler/scheduler_state_machine_unittest.cc

Index: cc/scheduler/scheduler_state_machine_unittest.cc
diff --git a/cc/scheduler/scheduler_state_machine_unittest.cc b/cc/scheduler/scheduler_state_machine_unittest.cc
index 71b1422b0366d41f043788ab45e7ff77bf472dd9..0a99a0969a0b4ab28055457e3102bed1093e44a5 100644
--- a/cc/scheduler/scheduler_state_machine_unittest.cc
+++ b/cc/scheduler/scheduler_state_machine_unittest.cc
@@ -181,9 +181,6 @@ class StateMachine : public SchedulerStateMachine {
   uint64_t last_begin_frame_sequence_number_pending_tree_was_fresh() const {
     return last_begin_frame_sequence_number_pending_tree_was_fresh_;
   }
-  uint64_t last_begin_frame_sequence_number_active_tree_was_fresh() const {
-    return last_begin_frame_sequence_number_active_tree_was_fresh_;
-  }
 
   using SchedulerStateMachine::ShouldTriggerBeginImplFrameDeadlineImmediately;
   using SchedulerStateMachine::ProactiveBeginFrameWanted;