Disable scheduler deadline task on battery power in Windows

cc/scheduler/scheduler_state_machine.cc

Index: cc/scheduler/scheduler_state_machine.cc
diff --git a/cc/scheduler/scheduler_state_machine.cc b/cc/scheduler/scheduler_state_machine.cc
index 74a4f0679f1adb7710278ef4a0bf32171e3db05a..4c6677132b0e50da3e63372557e5b9a965f2f5ea 100644
--- a/cc/scheduler/scheduler_state_machine.cc
+++ b/cc/scheduler/scheduler_state_machine.cc
@@ -48,7 +48,8 @@ SchedulerStateMachine::SchedulerStateMachine(const SchedulerSettings& settings)
       impl_latency_takes_priority_(false),
       skip_next_begin_main_frame_to_reduce_latency_(false),
       skip_begin_main_frame_to_reduce_latency_(false),
-      continuous_painting_(false) {
+      continuous_painting_(false),
+      on_battery_power_(false) {
 }
 
 const char* SchedulerStateMachine::OutputSurfaceStateToString(
@@ -238,6 +239,7 @@ void SchedulerStateMachine::AsValueInto(base::debug::TracedValue* state,
   state->SetBoolean("skip_next_begin_main_frame_to_reduce_latency",
                     skip_next_begin_main_frame_to_reduce_latency_);
   state->SetBoolean("continuous_painting", continuous_painting_);
+  state->SetBoolean("on_battery_power", on_battery_power_);
   state->EndDictionary();
 }
 
@@ -879,6 +881,11 @@ bool SchedulerStateMachine::ShouldTriggerBeginImplFrameDeadlineEarly() const {
   if (impl_latency_takes_priority_)
     return true;
 
+  // If we are on battery power and want to prioritize impl latency because
+  // we don't trust deadline tasks to execute at the right time.
+  if (settings_.prioritize_impl_latency_on_battery && on_battery_power_)

[danakj, 2014/10/09 21:18:02]

i'd say leave on_battery_power_ always false if the setting is off, ie don't set
up the listener when the setting if off.

otherwise you're adding a listener and setting states, but not to use them.

[sunnyps, 2014/10/09 22:04:39]

I agree. I'll rename on_battery_power_ to
impl_latency_takes_priority_on_battery_ so that it's clear that it takes both
the settings flag and power state into account. Also I believe that the name
"on_battery_power" might confuse someone if it doesn't actually reflect the
power state of the system and means something else. 

[danakj, 2014/10/09 22:08:27]

Eh, maybe it's fine to have it just be false when its not known. I don't find
the current name bad at all, but whatever you and the other scheduler folks
perfer :)

+    return true;
+
   return false;
 }