[es6] early error when Identifier is an escaped reserved word

src/messages.h

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // The infrastructure used for (localized) message reporting in V8.
 //
 // Note: there's a big unresolved issue about ownership of the data
 // structures used by this framework.
 
 #ifndef V8_MESSAGES_H_
@@ skipping 291 matching lines @@
   T(ForInOfLoopMultiBindings,                                                  \
     "Invalid left-hand side in % loop: Must have a single binding.")           \
   T(ForOfLoopInitializer,                                                      \
     "for-of loop variable declaration may not have an initializer.")           \
   T(IllegalAccess, "Illegal access")                                           \
   T(IllegalBreak, "Illegal break statement")                                   \
   T(IllegalContinue, "Illegal continue statement")                             \
   T(IllegalLanguageModeDirective,                                              \
     "Illegal '%' directive in function with non-simple parameter list")        \
   T(IllegalReturn, "Illegal return statement")                                 \
+  T(InvalidEscapedReservedWord, "Keyword must not contain escaped characters") \
   T(InvalidLhsInAssignment, "Invalid left-hand side in assignment")            \
   T(InvalidLhsInFor, "Invalid left-hand side in for-loop")                     \
   T(InvalidLhsInPostfixOp,                                                     \
     "Invalid left-hand side expression in postfix operation")                  \
   T(InvalidLhsInPrefixOp,                                                      \
     "Invalid left-hand side expression in prefix operation")                   \
   T(InvalidRegExpFlags, "Invalid flags supplied to RegExp constructor '%'")    \
   T(LabelRedeclaration, "Label '%' has already been declared")                 \
   T(MalformedArrowFunParamList, "Malformed arrow function parameter list")     \
   T(MalformedRegExp, "Invalid regular expression: /%/: %")                     \
@@ skipping 176 matching lines @@
   static MUST_USE_RESULT MaybeHandle<String> GetStringifiedProperty(
       Isolate* isolate, LookupIterator* property_lookup,
       Handle<String> default_value);
 
   List<Handle<JSObject> > visited_;
 };
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_MESSAGES_H_