[scheduler] Throttle default timer queue when renderer is backgrounded.

third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl.cc

Index: third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl.cc
diff --git a/third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl.cc b/third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl.cc
index 752e9a102cc6901281170bdc04c686c9ba2dd829..58a174e2afe420896bfc9c06583e8fbe01d0e81c 100644
--- a/third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl.cc
+++ b/third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl.cc
@@ -491,6 +491,9 @@ void RendererSchedulerImpl::OnRendererBackgrounded() {
   MainThreadOnly().foreground_main_thread_load_tracker.Pause(now);
   MainThreadOnly().background_main_thread_load_tracker.Resume(now);
 
+  task_queue_throttler()->IncreaseThrottleRefCount(

[alex clarke (OOO till 29th), 2016/12/06 18:20:12]

This is going to fight with UpdatePolicyLocked.

What you need to do (assuming Sami agrees this is a good idea - IIRC we
discussed this in the past and didn't do it for some reason) is:

1. Add this clause near the bottom of UpdatePolicyLocked:

if (MainThreadOnly().renderer_backgrounded) {
   new_policy.timer_queue_policy.time_domain_type = 
      TimeDomainType::THROTTLED;
}

2. Call ForceUpdatePolicy() in here and in OnRendererForegrounded

Note this needs to place nicely (i.e. not call ForceUpdatePolicy too often) with
SuspendTimerQueueWhenBackgrounded / ResumeTimerQueueWhenForegroundedOrResumed
which Jared added to suspend timers completely after 5 mins on android.

+      default_timer_task_runner_.get());
+
   if (!MainThreadOnly().timer_queue_suspension_when_backgrounded_enabled)
     return;
 
@@ -513,6 +516,9 @@ void RendererSchedulerImpl::OnRendererForegrounded() {
   MainThreadOnly().renderer_backgrounded = false;
   MainThreadOnly().renderer_suspended = false;
 
+  task_queue_throttler()->DecreaseThrottleRefCount(
+      default_timer_task_runner_.get());
+
   base::TimeTicks now = tick_clock()->NowTicks();
   MainThreadOnly().foreground_main_thread_load_tracker.Resume(now);
   MainThreadOnly().background_main_thread_load_tracker.Pause(now);