Replace HeapType with a non-templated FieldType class.

src/list.h

Index: src/list.h
diff --git a/src/list.h b/src/list.h
index 8b8a5dd1edd360e98396693f92f8cac8610752b2..83e5f4594ee5ae0bbdd0ac8d9f7337701c58a0c3 100644
--- a/src/list.h
+++ b/src/list.h
@@ -207,15 +207,13 @@ size_t GetMemoryUsedByList(const List<T, P>& list) {
 
 
 class Map;
-template<class> class TypeImpl;
-struct HeapTypeConfig;
-typedef TypeImpl<HeapTypeConfig> HeapType;
+class FieldType;
 class Code;
 template<typename T> class Handle;
 typedef List<Map*> MapList;
 typedef List<Code*> CodeList;
 typedef List<Handle<Map> > MapHandleList;
-typedef List<Handle<HeapType> > TypeHandleList;
+typedef List<Handle<FieldType> > TypeHandleList;
 typedef List<Handle<Code> > CodeHandleList;
 
 // Perform binary search for an element in an already sorted