Oilpan: fix build after r194911.

Source/core/style/StyleFetchedImage.h

Index: Source/core/style/StyleFetchedImage.h
diff --git a/Source/core/style/StyleFetchedImage.h b/Source/core/style/StyleFetchedImage.h
index e9f1f8c2435ec701403c19998c7961ba9a19791b..be1d5a006930c687334d426d18a07f2ac97dbc83 100644
--- a/Source/core/style/StyleFetchedImage.h
+++ b/Source/core/style/StyleFetchedImage.h
@@ -60,10 +60,10 @@ public:
     virtual ImageResource* cachedImage() const override { return m_image.get(); }
 
 private:
-    explicit StyleFetchedImage(ImageResource*, Document*);
+    StyleFetchedImage(ImageResource*, Document*);
 
     ResourcePtr<ImageResource> m_image;
-    RawPtrWillBeMember<Document> m_document;
+    RawPtrWillBePersistent<Document> m_document;
 };
 
 DEFINE_STYLE_IMAGE_TYPE_CASTS(StyleFetchedImage, isImageResource());