cc: Allow sending BeginMainFrame before draw or activation

cc/scheduler/scheduler_settings.cc

Index: cc/scheduler/scheduler_settings.cc
diff --git a/cc/scheduler/scheduler_settings.cc b/cc/scheduler/scheduler_settings.cc
index ad925d4d1359735a2d27baa2ee09641525adf92f..0aaa013556644a5389163fe57f83aa024a282114 100644
--- a/cc/scheduler/scheduler_settings.cc
+++ b/cc/scheduler/scheduler_settings.cc
@@ -8,6 +8,8 @@ namespace cc {
 
 SchedulerSettings::SchedulerSettings()
     : deadline_scheduling_enabled(true),
+      start_commit_before_draw_enabled(true),
+      start_commit_before_activate_enabled(false),

[Sami, 2014/02/18 18:45:50]

Should we dcheck in the scheduler constructor that
start_commit_before_activate_enabled implies start_commit_before_draw_enabled?
Just being paranoid :)

Also, maybe I missed it but should we have a test that explicitly turns on
start_commit_before_activate_enabled?

[brianderson, 2014/02/20 00:25:35]

A DCHECK sounds like a good idea.
I'll work on a scheduler unit test before landing. I'll probably avoid enabling
it in any of the layer tree tests until we might enable it by default.

       impl_side_painting(false),
       timeout_and_draw_when_animation_checkerboards(true),
       maximum_number_of_failed_draws_before_draw_is_forced_(3),