Add canExceedIdleDeadlineIfRequired function to Scheduler and use it in Oilpan

public/platform/WebScheduler.h

Index: public/platform/WebScheduler.h
diff --git a/public/platform/WebScheduler.h b/public/platform/WebScheduler.h
index a2cda3eac91603b1f741794377d01c942d88d16e..07a6e6a803e2bd2d17ab36260a6be62f93bd46dd 100644
--- a/public/platform/WebScheduler.h
+++ b/public/platform/WebScheduler.h
@@ -35,6 +35,11 @@ public:
     // Must be called on the main thread.
     virtual bool shouldYieldForHighPriorityWork() { return false; }
 
+    // Returns true if the deadline |deadlineSeconds| as passed to an IdleTask
+    // is the maximum possible idle task deadline duration which the scheduler
+    // will schedule.
+    virtual bool isMaximumIdleDeadline(double deadlineSeconds) { return false; }
+
     // Schedule an idle task to run the Blink main thread. For non-critical
     // tasks which may be reordered relative to other task types and may be
     // starved for an arbitrarily long time if no idle time is available.