Use a special EnumLength field to indicate number of valid enum cache values.

src/arm/lithium-arm.cc

Index: src/arm/lithium-arm.cc
diff --git a/src/arm/lithium-arm.cc b/src/arm/lithium-arm.cc
index 2ddabfc65b793f1103ed16ce7db8cfae09b9ccc6..aac7e8c324ee3f63e545e4ee0183b925d4a28a2f 100644
--- a/src/arm/lithium-arm.cc
+++ b/src/arm/lithium-arm.cc
@@ -1539,6 +1539,12 @@ LInstruction* LChunkBuilder::DoFixedArrayBaseLength(
 }
 
 
+LInstruction* LChunkBuilder::DoMapEnumLength(HMapEnumLength* instr) {
+  LOperand* map = UseRegisterAtStart(instr->value());
+  return DefineAsRegister(new(zone()) LMapEnumLength(map));
+}
+
+
 LInstruction* LChunkBuilder::DoElementsKind(HElementsKind* instr) {
   LOperand* object = UseRegisterAtStart(instr->value());
   return DefineAsRegister(new(zone()) LElementsKind(object));