[esnext] implement frontend changes for async/await proposal

src/parsing/token.h

 // Copyright 2012 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.
 
 #ifndef V8_PARSING_TOKEN_H_
 #define V8_PARSING_TOKEN_H_
 
 #include "src/base/logging.h"
 #include "src/globals.h"
 
@@ skipping 131 matching lines @@
   K(FALSE_LITERAL, "false", 0)                                       \
   T(NUMBER, NULL, 0)                                                 \
   T(SMI, NULL, 0)                                                    \
   T(STRING, NULL, 0)                                                 \
                                                                      \
   /* Identifiers (not keywords or future reserved words). */         \
   T(IDENTIFIER, NULL, 0)                                             \
                                                                      \
   /* Future reserved words (ECMA-262, section 7.6.1.2). */           \
   T(FUTURE_STRICT_RESERVED_WORD, NULL, 0)                            \
+  K(ASYNC, "async", 0)                                               \
   /* `await` is a reserved word in module code only */               \
   K(AWAIT, "await", 0)                                               \
   K(CLASS, "class", 0)                                               \
   K(CONST, "const", 0)                                               \
   K(ENUM, "enum", 0)                                                 \
   K(EXPORT, "export", 0)                                             \
   K(EXTENDS, "extends", 0)                                           \
   K(IMPORT, "import", 0)                                             \
   K(LET, "let", 0)                                                   \
   K(STATIC, "static", 0)                                             \
@@ skipping 32 matching lines @@
 
   // Predicates
   static bool IsKeyword(Value tok) {
     return token_type[tok] == 'K';
   }
 
   static bool IsIdentifier(Value tok, LanguageMode language_mode,
                            bool is_generator, bool is_module) {
     switch (tok) {
       case IDENTIFIER:
+      case ASYNC:
         return true;
       case ESCAPED_STRICT_RESERVED_WORD:
       case FUTURE_STRICT_RESERVED_WORD:
       case LET:
       case STATIC:
         return is_sloppy(language_mode);
       case YIELD:
         return !is_generator && is_sloppy(language_mode);
       case AWAIT:
         return !is_module;
@@ skipping 120 matching lines @@
   static const char* const name_[NUM_TOKENS];
   static const char* const string_[NUM_TOKENS];
   static const int8_t precedence_[NUM_TOKENS];
   static const char token_type[NUM_TOKENS];
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_PARSING_TOKEN_H_