[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..0a60891164c5c436411f60166cab109c7f78eafc 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
@@ -487,6 +487,8 @@ void RendererSchedulerImpl::OnRendererBackgrounded() {
 
   MainThreadOnly().renderer_backgrounded = true;
 
+  UpdatePolicy();
+
   base::TimeTicks now = tick_clock()->NowTicks();
   MainThreadOnly().foreground_main_thread_load_tracker.Pause(now);
   MainThreadOnly().background_main_thread_load_tracker.Resume(now);
@@ -513,6 +515,8 @@ void RendererSchedulerImpl::OnRendererForegrounded() {
   MainThreadOnly().renderer_backgrounded = false;
   MainThreadOnly().renderer_suspended = false;
 
+  UpdatePolicy();
+
   base::TimeTicks now = tick_clock()->NowTicks();
   MainThreadOnly().foreground_main_thread_load_tracker.Resume(now);
   MainThreadOnly().background_main_thread_load_tracker.Pause(now);
@@ -1073,6 +1077,9 @@ void RendererSchedulerImpl::UpdatePolicyLocked(UpdateType update_type) {
       ShouldDisableThrottlingBecauseOfAudio(now) ||
       MainThreadOnly().use_virtual_time;
 
+  if (MainThreadOnly().renderer_backgrounded)
+    new_policy.timer_queue_policy.time_domain_type = TimeDomainType::THROTTLED;

[Sami, 2016/12/06 19:09:10]

Should we have a TODO around making this also use the background time budget
pool? Ideally we'd get rid of this queue completely, but that might take awhile.

(Aside: we might also make it so that there's only one background budget pool
per renderer instead of one per WebView.)

[altimin, 2016/12/07 11:20:09]

Done. (And I want to state that I don't really like the idea of having one time
budget pool per renderer - it will prevent throttling when one of the pages is
foregrounded and it's against our frame performance isolation policy).

[Sami, 2016/12/07 19:24:49]

(Why would it prevent throttling? The foreground pages just wouldn't participate
in the budget. What I was mainly going for is that a renderer with 100 tabs
shouldn't necessarily be allowed to use more CPU than a renderer with 1 tab.
Later we can coalesce this limit across renderers too.)

+
   // Tracing is done before the early out check, because it's quite possible we
   // will otherwise miss this information in traces.
   CreateTraceEventObjectSnapshotLocked();