Change JSObject elements to be of type FixedArrayBase

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 2a22ade9686affa3fa50c31d124d78d4590af546..9b49115e26161b35625fbb0fae5c34949b4c246b 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -635,10 +635,11 @@ enum CompareResult {
                          WriteBarrierMode mode = UPDATE_WRITE_BARRIER); \
 
 
+class DictionaryElementsAccessor;
 class ElementsAccessor;
-class StringStream;
+class FixedArrayBase;
 class ObjectVisitor;
-class DictionaryElementsAccessor;
+class StringStream;
 
 struct ValueInfo : public Malloced {
   ValueInfo() : type(FIRST_TYPE), ptr(NULL), str(NULL), number(0) { }
@@ -1492,7 +1493,7 @@ class JSObject: public JSReceiver {
   // In the slow mode the elements is either a NumberDictionary, an
   // ExternalArray, or a FixedArray parameter map for a (non-strict)
   // arguments object.
-  DECL_ACCESSORS(elements, HeapObject)
+  DECL_ACCESSORS(elements, FixedArrayBase)
   inline void initialize_elements();
   MUST_USE_RESULT inline MaybeObject* ResetElements();
   inline ElementsKind GetElementsKind();