Rename IdleCallbackDeadline to IdleDeadline to be in sync with spec.

Source/core/dom/IdleRequestCallback.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 IdleRequestCallback_h
 #define IdleRequestCallback_h
 
 #include "core/dom/ScriptedIdleTaskController.h"
 #include "platform/Timer.h"
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
 class IdleCallbackDeadline;
 
 class IdleRequestCallback : public GarbageCollectedFinalized<IdleRequestCallback> {
 public:
     DEFINE_INLINE_VIRTUAL_TRACE() {}
     virtual ~IdleRequestCallback() {}
 
-    virtual void handleEvent(IdleCallbackDeadline*) = 0;
+    virtual void handleEvent(IdleDeadline*) = 0;
 };
 }
 
 #endif // IdleRequestCallback_h