cc: Allow sending BeginMainFrame before draw or activation

cc/scheduler/scheduler.cc

Index: cc/scheduler/scheduler.cc
diff --git a/cc/scheduler/scheduler.cc b/cc/scheduler/scheduler.cc
index 25ba5726f37bad7b9a6f13503da61d6baecb90ac..1828348229c59061feb23ac7f7b8a9f7e1b8ea0a 100644
--- a/cc/scheduler/scheduler.cc
+++ b/cc/scheduler/scheduler.cc
@@ -27,6 +27,9 @@ Scheduler::Scheduler(SchedulerClient* client,
       weak_factory_(this) {
   DCHECK(client_);
   DCHECK(!state_machine_.BeginImplFrameNeeded());
+  if (settings_.start_commit_before_activate_enabled) {
+    DCHECK(settings_.start_commit_before_draw_enabled);
+  }
 }
 
 Scheduler::~Scheduler() {}