WIP [esnext] implement async iteration proposal

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 455 matching lines @@
   T(StrictCannotAssign, "Cannot assign to read only '%' in strict mode")       \
   T(StrictDeleteProperty, "Cannot delete property '%' of %")                   \
   T(StrictPoisonPill,                                                          \
     "'caller', 'callee', and 'arguments' properties may not be accessed on "   \
     "strict mode functions or the arguments objects for calls to them")        \
   T(StrictReadOnlyProperty,                                                    \
     "Cannot assign to read only property '%' of % '%'")                        \
   T(StrictCannotCreateProperty, "Cannot create property '%' on % '%'")         \
   T(SymbolIteratorInvalid,                                                     \
     "Result of the Symbol.iterator method is not an object")                   \
+  T(SymbolAsyncIteratorInvalid,                                                \
+    "Result of the Symbol.asyncIterator method is not an object")              \
   T(SymbolKeyFor, "% is not a symbol")                                         \
   T(SymbolToNumber, "Cannot convert a Symbol value to a number")               \
   T(SymbolToString, "Cannot convert a Symbol value to a string")               \
   T(SimdToNumber, "Cannot convert a SIMD value to a number")                   \
   T(ThrowMethodMissing, "The iterator does not provide a 'throw' method.")     \
   T(UndefinedOrNullToObject, "Cannot convert undefined or null to object")     \
   T(ValueAndAccessor,                                                          \
     "Invalid property descriptor. Cannot both specify accessors and a value "  \
     "or writable attribute, %")                                                \
   T(VarRedeclaration, "Identifier '%' has already been declared")              \
@@ skipping 243 matching lines @@
                                         const MessageLocation* loc,
                                         Handle<Object> message_obj,
                                         v8::Local<v8::Value> api_exception_obj);
 };
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_MESSAGES_H_