Add canExceedIdleDeadlineIfRequired function to Scheduler and use it in Oilpan

Source/platform/scheduler/Scheduler.h

Index: Source/platform/scheduler/Scheduler.h
diff --git a/Source/platform/scheduler/Scheduler.h b/Source/platform/scheduler/Scheduler.h
index a18621d0e3705e7d592434b7b4ad09e961158f18..5f13481e1d28a8a147e6c5c5f8ea420024c7ef97 100644
--- a/Source/platform/scheduler/Scheduler.h
+++ b/Source/platform/scheduler/Scheduler.h
@@ -45,6 +45,11 @@ public:
     // Must be called on the main thread.
     bool shouldYieldForHighPriorityWork() const;
 
+    // Returns true if the deadline |deadlineSeconds| as passed to an IdleTask
+    // is the maximum possible idle task deadline duration which the scheduler
+    // will schedule.
+    bool isMaximumIdleDeadline(double deadlineSeconds) const;
+
 protected:
     Scheduler(WebScheduler*);
     virtual ~Scheduler();