cc: Control activation from the Scheduler

cc/scheduler/scheduler.h

Index: cc/scheduler/scheduler.h
diff --git a/cc/scheduler/scheduler.h b/cc/scheduler/scheduler.h
index c64dad0f23e24a74fa5f4fd902efa09fa576bf29..6c6ccca054b2e1730bf51260df15b2e4b9cf2454 100644
--- a/cc/scheduler/scheduler.h
+++ b/cc/scheduler/scheduler.h
@@ -41,7 +41,7 @@ class SchedulerClient {
   ScheduledActionDrawAndSwapForced() = 0;
   virtual void ScheduledActionCommit() = 0;
   virtual void ScheduledActionUpdateVisibleTiles() = 0;
-  virtual void ScheduledActionActivatePendingTreeIfNeeded() = 0;
+  virtual void ScheduledActionActivatePendingTree() = 0;
   virtual void ScheduledActionBeginOutputSurfaceCreation() = 0;
   virtual void ScheduledActionAcquireLayerTexturesForMainThread() = 0;
   virtual void DidAnticipatedDrawTimeChange(base::TimeTicks time) = 0;
@@ -67,7 +67,8 @@ class CC_EXPORT Scheduler {
 
   void SetVisible(bool visible);
   void SetCanDraw(bool can_draw);
-  void SetHasPendingTree(bool has_pending_tree);
+  void NotifyReadyToActivate();
+  void SetHasTrees(bool has_pending_tree,  bool active_tree_is_null);

[reveman, 2013/08/23 16:16:48]

has_active_tree? find it confusing that active tree flags is inverted but not
the pending tree flag.

[enne (OOO), 2013/08/23 17:54:09]

Doesn't the scheduler already know this information?  For example, the
commit_results_in_pending_tree that you added in the other patch.  It seems like
either the Scheduler should assume the tree state based on commit/activate/abort
actions or it should be told explicitly, but not a little of both.

[brianderson, 2013/08/23 18:17:38]

Hmm. I used active_tree_is_null because, technically, there is an active tree in
LTHI, it's just that it's root layer is null. From the point of view of the
Scheduler though, we might as well use has_active_tree.  I'll change it if we
are going to keep it.

[brianderson, 2013/08/23 18:17:38]

Is it safe to assume that the active tree's root layer is not null after the
first commit/activation for the lifetime of the Scheduler class?

[enne (OOO), 2013/08/23 18:30:35]

Ok, good point.  I don't think we do, but I think it's technically possible.

That said, it seems like you're only using active_tree_is_null to check in
ShouldActivatePendingTree() to avoid spurious aborted draws before the first
activation.  You could maybe replace that with bool has_ever_activated_, which
the scheduler definitely knows about.

 
   void SetNeedsCommit();