Oilpan: fix build after r185817.

Source/core/fetch/ResourceFetcher.cpp

Index: Source/core/fetch/ResourceFetcher.cpp
diff --git a/Source/core/fetch/ResourceFetcher.cpp b/Source/core/fetch/ResourceFetcher.cpp
index 71f753be2c7109ef2845f96e7b638d3e5b03ba16..a947bbd4f0975c4eae3a2d88c35bfa1eb0762465 100644
--- a/Source/core/fetch/ResourceFetcher.cpp
+++ b/Source/core/fetch/ResourceFetcher.cpp
@@ -1311,7 +1311,7 @@ void ResourceFetcher::clearPreloads()
 void ResourceFetcher::didFinishLoading(Resource* resource, double finishTime, int64_t encodedDataLength)
 {
     TRACE_EVENT_ASYNC_END0("net", "Resource", resource);
-    RefPtr<Document> protectDocument(m_document);
+    RefPtrWillBeRawPtr<Document> protectDocument(document());
     RefPtr<DocumentLoader> protectDocumentLoader(m_documentLoader);
 
     if (resource && resource->response().isHTTP() && resource->response().httpStatusCode() < 400 && document()) {