Oilpan: avoid using WeakPtr<> for heap residing objects.

Source/modules/fetch/GlobalFetch.h

 // Copyright 2014 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 GlobalFetch_h
 #define GlobalFetch_h
 
 #include "bindings/core/v8/ScriptPromise.h"
 #include "modules/ModulesExport.h"
 #include "modules/fetch/Request.h"
 #include "wtf/WeakPtr.h"
 
 namespace blink {
 
 class Dictionary;
 class DOMWindow;
 class ExceptionState;
 class ScriptState;
 class WorkerGlobalScope;
 
 class GlobalFetch {
 public:
-    class MODULES_EXPORT ScopedFetcher {
+    class MODULES_EXPORT ScopedFetcher : public WillBeGarbageCollectedMixin {
     public:
         virtual ~ScopedFetcher();
 
         virtual ScriptPromise fetch(ScriptState*, const RequestInfo&, const Dictionary&, ExceptionState&) = 0;
 
-        static WeakPtr<ScopedFetcher> from(DOMWindow&);
-        static WeakPtr<ScopedFetcher> from(WorkerGlobalScope&);
+        static WeakPtrWillBeRawPtr<ScopedFetcher> from(DOMWindow&);
+        static WeakPtrWillBeRawPtr<ScopedFetcher> from(WorkerGlobalScope&);
 
         DECLARE_VIRTUAL_TRACE();
     };
 
     static ScriptPromise fetch(ScriptState*, DOMWindow&, const RequestInfo&, const Dictionary&, ExceptionState&);
     static ScriptPromise fetch(ScriptState*, WorkerGlobalScope&, const RequestInfo&, const Dictionary&, ExceptionState&);
 };
 
 } // namespace blink
 
 #endif // GlobalFetch_h