Added support for ES5's propertyname production.

src/token.h

Index: src/token.h
diff --git a/src/token.h b/src/token.h
index 2a228d67cf422f2b6dd623e2105ea082f4595b5e..0d8960b8ee48ad4bc84cd5f5f4d50c4ac7075167 100644
--- a/src/token.h
+++ b/src/token.h
@@ -220,6 +220,10 @@ class Token {
   }
 
   // Predicates
+  static bool IsKeyword(Value tok) {
+    return token_type[tok] == 'K';
+  }
+
   static bool IsAssignmentOp(Value tok) {
     return INIT_VAR <= tok && tok <= ASSIGN_MOD;
   }
@@ -263,6 +267,7 @@ class Token {
   static const char* name_[NUM_TOKENS];
   static const char* string_[NUM_TOKENS];
   static int8_t precedence_[NUM_TOKENS];
+  static const char token_type[NUM_TOKENS];
 };
 
 } }  // namespace v8::internal