Rename IdleCallbackDeadline to IdleDeadline to be in sync with spec.

Source/core/dom/IdleCallbackDeadline.cpp

-// 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.
-
-#include "config.h"
-#include "core/dom/IdleCallbackDeadline.h"
-
-#include "wtf/CurrentTime.h"
-
-namespace blink {
-
-IdleCallbackDeadline::IdleCallbackDeadline(double deadlineSeconds, CallbackType callbackType)
-    : m_deadlineSeconds(deadlineSeconds)
-    , m_callbackType(callbackType)
-{
-}
-
-double IdleCallbackDeadline::timeRemaining() const
-{
-    double timeRemaining = m_deadlineSeconds - monotonicallyIncreasingTime();
-    if (timeRemaining < 0)
-        timeRemaining = 0;
-
-    return timeRemaining * 1000;
-}
-
-} // namespace blink