[scheduler] Implement time-based cpu throttling.

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

Index: third_party/WebKit/public/platform/scheduler/base/task_queue.h
diff --git a/third_party/WebKit/public/platform/scheduler/base/task_queue.h b/third_party/WebKit/public/platform/scheduler/base/task_queue.h
index de0d22ce45eb4f5bf4373b8beef0c3378ac7b9c4..8e51e02524d40ac53796f0b0ed8d26ea9568c450 100644
--- a/third_party/WebKit/public/platform/scheduler/base/task_queue.h
+++ b/third_party/WebKit/public/platform/scheduler/base/task_queue.h
@@ -7,7 +7,9 @@
 
 #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 {
@@ -144,10 +146,29 @@ class BLINK_PLATFORM_EXPORT TaskQueue : public base::SingleThreadTaskRunner {
   // 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;
+
   // Can be called on any thread.
   virtual const char* GetName() const = 0;