[scheduler] Implement time-based cpu throttling.

third_party/WebKit/public/platform/scheduler/base/task_queue.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef THIRD_PARTY_WEBKIT_PUBLIC_PLATFORM_SCHEDULER_BASE_TASK_QUEUE_H_
 #define THIRD_PARTY_WEBKIT_PUBLIC_PLATFORM_SCHEDULER_BASE_TASK_QUEUE_H_
 
 #include "base/macros.h"
 #include "base/message_loop/message_loop.h"
+#include "base/optional.h"
 #include "base/single_thread_task_runner.h"
+#include "base/time/time.h"
 #include "public/platform/WebCommon.h"
 
 namespace base {
 namespace trace_event {
 class BlameContext;
 }
 }
 
 namespace blink {
 namespace scheduler {
@@ skipping 116 matching lines @@
   // Enable or disable task execution for this queue. NOTE this must be called
   // on the thread this TaskQueue was created by.
   virtual void SetQueueEnabled(bool enabled) = 0;
 
   // NOTE this must be called on the thread this TaskQueue was created by.
   virtual bool IsQueueEnabled() const = 0;
 
   // Returns true if the queue is completely empty.
   virtual bool IsEmpty() const = 0;
 
-  // Returns true if the queue has work that's ready to execute now. NOTE this
-  // must be called on the thread this TaskQueue was created by.
+  // Returns true if the queue has work that's ready to execute now.
+  // NOTE: this must be called on the thread this TaskQueue was created by.
   virtual bool HasPendingImmediateWork() const = 0;
 
+  // Returns requested run time of next delayed task, which is not ready
+  // to run. If there are no such tasks, returns base::nullopt.
+  // NOTE: this must be called on the thread this TaskQueue was created by.
+  virtual base::Optional<base::TimeTicks> GetNextScheduledWakeUp() = 0;
+
+  // Returns next point in time when the task from this queue is ready to run.
+  // (now if there are immediate tasks or ready delayed task, run time
+  // of earliest delayed task otherwise).
+  // Returns base::nullopt if there are no tasks in this queue.
+  //
+  // NOTE: This function call is approximately equivalent to following:
+  // if (HasPendingImmediateWork())
+  //    return Now();
+  // return GetNextScheduledWakeUp();
+  // Difference is that GetNextTaskRunTime behaves "atomically" i.e.
+  // it avoids problem when task becomes ready immediately after
+  // HasPendingImmediateWork.
+  virtual base::Optional<base::TimeTicks> GetNextTaskRunTime() = 0;

[alex clarke (OOO till 29th), 2016/09/14 12:36:34]

No please don't put this here.  It's confusing from an interface point of view.

[altimin, 2016/09/14 18:34:50]

Done.

+
   // Can be called on any thread.
   virtual const char* GetName() const = 0;
 
   // Set the priority of the queue to |priority|. NOTE this must be called on
   // the thread this TaskQueue was created by.
   virtual void SetQueuePriority(QueuePriority priority) = 0;
 
   // Returns the current queue priority.
   virtual QueuePriority GetQueuePriority() const = 0;
 
@@ skipping 33 matching lines @@
  protected:
   ~TaskQueue() override {}
 
   DISALLOW_COPY_AND_ASSIGN(TaskQueue);
 };
 
 }  // namespace scheduler
 }  // namespace blink
 
 #endif  // THIRD_PARTY_WEBKIT_PUBLIC_PLATFORM_SCHEDULER_BASE_TASK_QUEUE_H_