Re-apply r5165 (Added support for ES5's propertyname production)...

src/token.h

Index: src/token.h
===================================================================
--- src/token.h	(revision 5191)
+++ src/token.h	(working copy)
@@ -220,6 +220,10 @@
   }
 
   // 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 @@
   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