Oilpan: fix build after r192918.

Source/core/dom/FrameRequestCallbackCollection.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 FrameRequestCallbackCollection_h
 #define FrameRequestCallbackCollection_h
 
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
 class ExecutionContext;
 class FrameRequestCallback;
 
 class FrameRequestCallbackCollection final {
+    DISALLOW_ALLOCATION();
 public:
     explicit FrameRequestCallbackCollection(ExecutionContext*);
 
-    typedef int CallbackId;
+    using CallbackId = int;
     CallbackId registerCallback(FrameRequestCallback*);
     void cancelCallback(CallbackId);
     void executeCallbacks(double highResNowMs, double highResNowMsLegacy);
 
     bool isEmpty() const { return !m_callbacks.size(); }
 
     DECLARE_TRACE();
 
 private:
-    typedef PersistentHeapVectorWillBeHeapVector<Member<FrameRequestCallback>> CallbackList;
+    using CallbackList = PersistentHeapVectorWillBeHeapVector<Member<FrameRequestCallback>>;
     CallbackList m_callbacks;
     CallbackList m_callbacksToInvoke; // only non-empty while inside executeCallbacks
 
     CallbackId m_nextCallbackId = 0;
 
-    ExecutionContext* m_context = nullptr;
+    RawPtrWillBeMember<ExecutionContext> m_context;
 };
 
 } // namespace blink
 
 #endif // FrameRequestCallbackCollection_h