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

src/arm/lithium-arm.h

Index: src/arm/lithium-arm.h
diff --git a/src/arm/lithium-arm.h b/src/arm/lithium-arm.h
index 782dd617583f688d1885cec813f40d289acd593f..e6e102f7620042141a13034a137489e01bd6c753 100644
--- a/src/arm/lithium-arm.h
+++ b/src/arm/lithium-arm.h
@@ -132,6 +132,7 @@ class LCodeGen;
   V(LoadNamedField)                             \
   V(LoadNamedFieldPolymorphic)                  \
   V(LoadNamedGeneric)                           \
+  V(MapEnumLength)                              \
   V(MathFloorOfDiv)                             \
   V(MathMinMax)                                 \
   V(ModI)                                       \
@@ -1002,6 +1003,16 @@ class LFixedArrayBaseLength: public LTemplateInstruction<1, 1, 0> {
 };
 
 
+class LMapEnumLength: public LTemplateInstruction<1, 1, 0> {
+ public:
+  explicit LMapEnumLength(LOperand* value) {
+    inputs_[0] = value;
+  }
+
+  DECLARE_CONCRETE_INSTRUCTION(MapEnumLength, "map-enum-length")
+};
+
+
 class LElementsKind: public LTemplateInstruction<1, 1, 0> {
  public:
   explicit LElementsKind(LOperand* value) {