Oilpan: Remove guardRef and guardDeref from TreeScope.

Source/core/html/imports/HTMLImportChild.h

Index: Source/core/html/imports/HTMLImportChild.h
diff --git a/Source/core/html/imports/HTMLImportChild.h b/Source/core/html/imports/HTMLImportChild.h
index 50c74f46d4ac8fc051d7479cc1046bc05f464833..633114f41e57c3d74afc72dde5f26e32d58324c4 100644
--- a/Source/core/html/imports/HTMLImportChild.h
+++ b/Source/core/html/imports/HTMLImportChild.h
@@ -34,6 +34,7 @@
 #include "core/fetch/RawResource.h"
 #include "core/fetch/ResourceOwner.h"
 #include "core/html/imports/HTMLImport.h"
+#include "heap/Handle.h"
 #include "platform/weborigin/KURL.h"
 #include "wtf/Vector.h"
 
@@ -98,7 +99,11 @@ private:
     void shareLoader(HTMLImportChild*);
     void ensureLoader();
 
+#if ENABLE(OILPAN)
+    Persistent<Document> m_master;
+#else
     Document& m_master;
+#endif
     KURL m_url;
     CustomElementMicrotaskImportStep* m_customElementMicrotaskStep;
     HTMLImportLoader* m_loader;