Allow ui::Compositor to disable commits during tab-switch

ui/compositor/compositor.cc

Index: ui/compositor/compositor.cc
diff --git a/ui/compositor/compositor.cc b/ui/compositor/compositor.cc
index 6293c2c19cf6d6e2fbb2fda6a548b18226e15cfa..f1758cee5ba810d7b2602c300404e64955af9480 100644
--- a/ui/compositor/compositor.cc
+++ b/ui/compositor/compositor.cc
@@ -76,7 +76,6 @@ Compositor::Compositor(gfx::AcceleratedWidget widget,
       device_scale_factor_(0.0f),
       last_started_frame_(0),
       last_ended_frame_(0),
-      disable_schedule_composite_(false),
       compositor_lock_(NULL),
       layer_animator_collection_(this),
       weak_ptr_factory_(this) {
@@ -294,12 +293,8 @@ void Compositor::BeginMainFrameNotExpectedSoon() {
 }
 
 void Compositor::Layout() {
-  // We're sending damage that will be addressed during this composite
-  // cycle, so we don't need to schedule another composite to address it.
-  disable_schedule_composite_ = true;
   if (root_layer_)
     root_layer_->SendDamagedRects();
-  disable_schedule_composite_ = false;
 }
 
 void Compositor::RequestNewOutputSurface() {
@@ -330,6 +325,10 @@ void Compositor::DidCompleteSwapBuffers() {
                     OnCompositingEnded(this));
 }
 
+void Compositor::SetDeferCommits(bool defer_commits) {
+  host_->SetDeferCommits(defer_commits);

[danakj, 2015/03/11 17:22:55]

You'll now have a state where commits are deferred but IsLocked() will return
false. Is that going to be weird?

I was expecting that you used the lock but just let your code remove the
timeout. But maybe this is okay. Can you give me some confidence in this
potential pitfall?

[ccameron, 2015/03/11 21:46:43]

The timeout for the lock is only so that the UI doesn't hang ... that's not a
concern for Mac (ui::Compositor doesn't draw the UI), so I added something a
flag to disable the timeout and just use a CompositorLock.

+}
+
 void Compositor::DidPostSwapBuffers() {
   base::TimeTicks start_time = gfx::FrameTime::Now();
   FOR_EACH_OBSERVER(CompositorObserver, observer_list_,