[scheduler] Implement time-based cpu throttling.

third_party/WebKit/Source/platform/scheduler/base/task_queue_impl.h

Index: third_party/WebKit/Source/platform/scheduler/base/task_queue_impl.h
diff --git a/third_party/WebKit/Source/platform/scheduler/base/task_queue_impl.h b/third_party/WebKit/Source/platform/scheduler/base/task_queue_impl.h
index 71f4103a4b82445237f6de8c6352580d25c34611..016ea609f468449db0d039385b005a4298e7b0e2 100644
--- a/third_party/WebKit/Source/platform/scheduler/base/task_queue_impl.h
+++ b/third_party/WebKit/Source/platform/scheduler/base/task_queue_impl.h
@@ -149,6 +149,8 @@ class BLINK_PLATFORM_EXPORT TaskQueueImpl final : public TaskQueue {
   bool IsQueueEnabled() const override;
   bool IsEmpty() const override;
   bool HasPendingImmediateWork() const override;
+  base::Optional<base::TimeTicks> GetNextScheduledWakeUp() override;
+  base::Optional<base::TimeTicks> GetNextTaskRunTime() override;

[alex clarke (OOO till 29th), 2016/09/12 17:45:26]

I'm fine with adding GetNextScheduledWakeUp but I'm not keen on
GetNextTaskRunTime being part of the TaskQueue API for these reasons:

1. It's too similar to GetNextScheduledWakeUp.  How would you know which to
call?
2. You can simulate it with HasPendingImmediateWork() plus
GetNextScheduledWakeUp()

I'd suggest moving the logic into a helper inside TaskQueueThrottler.

[altimin, 2016/09/14 11:23:15]

I added a comment about this in TaskQueue itself, copying it here:

Difference is that GetNextTaskRunTime behaves "atomically" i.e.
it avoids problem when task becomes ready immediately after
HasPendingImmediateWork.

   void SetQueuePriority(QueuePriority priority) override;
   QueuePriority GetQueuePriority() const override;
   void AddTaskObserver(base::MessageLoop::TaskObserver* task_observer) override;
@@ -293,6 +295,9 @@ class BLINK_PLATFORM_EXPORT TaskQueueImpl final : public TaskQueue {
   static void TaskAsValueInto(const Task& task,
                               base::trace_event::TracedValue* state);
 
+  // Same as public version, but uses given LazyNow.
+  bool HasPendingImmediateWork(LazyNow* lazy_now) const;
+
   const base::PlatformThreadId thread_id_;
 
   mutable base::Lock any_thread_lock_;