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

Source/modules/fetch/GlobalFetch.h

Index: Source/modules/fetch/GlobalFetch.h
diff --git a/Source/modules/fetch/GlobalFetch.h b/Source/modules/fetch/GlobalFetch.h
index db1e6b5f7eb2eb1b66b4fab1e1ef1857ca9d5242..81bbe611a4c39a646a76e4313a365634119b894f 100644
--- a/Source/modules/fetch/GlobalFetch.h
+++ b/Source/modules/fetch/GlobalFetch.h
@@ -20,14 +20,14 @@ 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();
     };