Added ability to dynamically toggle frame throttling in the scheduler.

cc/scheduler/scheduler.cc

Index: cc/scheduler/scheduler.cc
diff --git a/cc/scheduler/scheduler.cc b/cc/scheduler/scheduler.cc
index 143c3ff54489573b1e22bf3a2a35ee17fecb1d95..57366e04a1254c123cb7f12dc66053f34e88b8aa 100644
--- a/cc/scheduler/scheduler.cc
+++ b/cc/scheduler/scheduler.cc
@@ -71,6 +71,17 @@ SchedulerFrameSourcesConstructor::ConstructBackgroundFrameSource(
   return scheduler->background_frame_source_internal_.get();
 }
 
+BeginFrameSource*
+SchedulerFrameSourcesConstructor::ConstructUnthrottledFrameSource(
+    Scheduler* scheduler) {
+  TRACE_EVENT1("cc", "Scheduler::Scheduler()", "PrimaryFrameSource",
+               "BackToBackBeginFrameSource");
+  DCHECK(!scheduler->unthrottled_frame_source_internal_);
+  scheduler->unthrottled_frame_source_internal_ =
+      BackToBackBeginFrameSource::Create(scheduler->task_runner_.get());
+  return scheduler->unthrottled_frame_source_internal_.get();
+}
+
 Scheduler::Scheduler(
     SchedulerClient* client,
     const SchedulerSettings& scheduler_settings,
@@ -85,6 +96,7 @@ Scheduler::Scheduler(
       primary_frame_source_internal_(external_begin_frame_source.Pass()),
       background_frame_source_internal_(),
       vsync_observer_(NULL),
+      throttle_frame_production_(scheduler_settings.throttle_frame_production),
       settings_(scheduler_settings),
       client_(client),
       layer_tree_host_id_(layer_tree_host_id),
@@ -125,6 +137,11 @@ Scheduler::Scheduler(
       frame_sources_constructor->ConstructBackgroundFrameSource(this);
   frame_source_->AddSource(background_frame_source_);
 
+  // Unthrottled frame source
+  unthrottled_frame_source_ =
+      frame_sources_constructor->ConstructUnthrottledFrameSource(this);
+  frame_source_->AddSource(unthrottled_frame_source_);
+
   SetupPowerMonitoring();
 }
 
@@ -184,16 +201,24 @@ void Scheduler::SetCanStart() {
   ProcessScheduledActions();
 }
 
-void Scheduler::SetVisible(bool visible) {
-  state_machine_.SetVisible(visible);
-  if (visible) {
-    frame_source_->SetActiveSource(primary_frame_source_);
+void Scheduler::UpdateActiveFrameSource() {
+  if (state_machine_.visible()) {
+    if (throttle_frame_production_) {
+      frame_source_->SetActiveSource(primary_frame_source_);
+    } else {
+      frame_source_->SetActiveSource(unthrottled_frame_source_);
+    }
   } else {
     frame_source_->SetActiveSource(background_frame_source_);
   }
   ProcessScheduledActions();
 }
 
+void Scheduler::SetVisible(bool visible) {
+  state_machine_.SetVisible(visible);
+  UpdateActiveFrameSource();
+}
+
 void Scheduler::SetCanDraw(bool can_draw) {
   state_machine_.SetCanDraw(can_draw);
   ProcessScheduledActions();
@@ -209,6 +234,11 @@ void Scheduler::NotifyReadyToDraw() {
   // crbugs 352894, 383157, 421923.
 }
 
+void Scheduler::SetThrottleFrameProduction(bool throttle) {
+  throttle_frame_production_ = settings_.throttle_frame_production && throttle;

[enne (OOO), 2014/12/15 23:21:07]

It's a little odd to my eyes to have both a scheduler setting and a toggle
function.  Could you just have the toggle function?  What's the setting for?

[brianderson, 2014/12/16 22:36:42]

Can we make the command line flag only set the initial state of
throttle_frame_production_ and the dev tools setting?

+  UpdateActiveFrameSource();
+}
+
 void Scheduler::SetNeedsCommit() {
   state_machine_.SetNeedsCommit();
   ProcessScheduledActions();