Add complete ElementKind information directly to Map for objects with elements.

src/x64/macro-assembler-x64.cc

Index: src/x64/macro-assembler-x64.cc
diff --git a/src/x64/macro-assembler-x64.cc b/src/x64/macro-assembler-x64.cc
index 2d2857951556cca3009a7a98643bbd619bbfae3b..0fc75028b304bd965d9b937e2b70155d61134a5c 100644
--- a/src/x64/macro-assembler-x64.cc
+++ b/src/x64/macro-assembler-x64.cc
@@ -2558,6 +2558,16 @@ void MacroAssembler::CmpInstanceType(Register map, InstanceType type) {
 }
 
 
+void MacroAssembler::CheckFastElements(Register map,
+                                       Label* fail,
+                                       Label::Distance distance) {
+  STATIC_ASSERT(JSObject::FAST_ELEMENTS == 0);
+  cmpb(FieldOperand(map, Map::kBitField2Offset),
+       Immediate(Map::kMaximumBitField2FastElementValue));
+  j(above, fail, distance);
+}
+
+
 void MacroAssembler::CheckMap(Register obj,
                               Handle<Map> map,
                               Label* fail,