Experimental 'purging and suspending' backgrounded tabs behind the flag

components/scheduler/renderer/renderer_scheduler_impl.cc

Index: components/scheduler/renderer/renderer_scheduler_impl.cc
diff --git a/components/scheduler/renderer/renderer_scheduler_impl.cc b/components/scheduler/renderer/renderer_scheduler_impl.cc
index f241d7bb755b5c2ca1f66aeb42c9d38581ed7d3f..9f3bbd9548f009fe8ebf06d7e356474dcacbcc0e 100644
--- a/components/scheduler/renderer/renderer_scheduler_impl.cc
+++ b/components/scheduler/renderer/renderer_scheduler_impl.cc
@@ -384,6 +384,14 @@ void RendererSchedulerImpl::OnRendererForegrounded() {
   ResumeTimerQueueWhenForegrounded();
 }
 
+void RendererSchedulerImpl::OnRendererPurgeAndSuspend() {
+  helper_.CheckOnValidThread();
+  if (helper_.IsShutdown() || !MainThreadOnly().renderer_backgrounded)

[Sami, 2016/04/27 15:44:43]

We should probably cancel suspend_timers_when_backgrounded_closure_ here because
this is doing essentially the same thing.

[hajimehoshi, 2016/04/28 10:26:58]

Done.

+    return;
+  // TODO(hajimehoshi): Implement purging e.g. cache (crbug/607077)

[Sami, 2016/04/27 15:44:43]

Have you thought about what kind of interfaces would you need to implement
purging? Since this is in components it might be a little awkward. (One proposal
has been to move RendererScheduler to blink/platform, but so far we haven't
investigated it too deeply.)

[hajimehoshi, 2016/04/28 10:26:58]

Right. Moved this comment to RenderThreadImpl and changed the scheduler to do
only suspending. Done.

+  SuspendTimerQueueWhenBackgrounded();

[Sami, 2016/04/27 15:44:43]

We should think about whether we need to suspend other task sources such as
network tasks and perhaps postMessages.

[hajimehoshi, 2016/04/28 10:26:58]

Good point, we might need to do what you suggest. However, we expect suspending
only the timer queue will stop not all but most of layout and JavaScript. I'll
revisit this when needed since this is just an experiment.

+}
+
 void RendererSchedulerImpl::EndIdlePeriod() {
   if (MainThreadOnly().in_idle_period_for_testing)
     return;