Introduce some predicates over variable modes.

src/variables.h

Index: src/variables.h
diff --git a/src/variables.h b/src/variables.h
index c49bab95da2a7aa9cfab87432bd4089ce2b3349f..ba26b80472c0b409f28074e46638824cc79543f8 100644
--- a/src/variables.h
+++ b/src/variables.h
@@ -120,15 +120,8 @@ class Variable: public ZoneObject {
   bool IsLookupSlot() const { return location_ == LOOKUP; }
   bool IsGlobalObjectProperty() const;
 
-  bool is_dynamic() const {
-    return (mode_ == DYNAMIC ||
-            mode_ == DYNAMIC_GLOBAL ||
-            mode_ == DYNAMIC_LOCAL);
-  }
-  bool is_const_mode() const {
-    return (mode_ == CONST ||
-            mode_ == CONST_HARMONY);
-  }
+  bool is_dynamic() const { return IsDynamicVariableMode(mode_); }
+  bool is_const_mode() const { return IsImmutableVariableMode(mode_); }
   bool binding_needs_init() const {
     return initialization_flag_ == kNeedsInitialization;
   }