[es7] Implement async functions parsing

src/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_TOKEN_H_
 #define V8_TOKEN_H_
 
 #include "src/base/logging.h"
 #include "src/globals.h"
 
@@ skipping 143 matching lines @@
   K(CLASS, "class", 0)                                               \
   K(CONST, "const", 0)                                               \
   K(EXPORT, "export", 0)                                             \
   K(EXTENDS, "extends", 0)                                           \
   K(IMPORT, "import", 0)                                             \
   K(LET, "let", 0)                                                   \
   K(STATIC, "static", 0)                                             \
   K(YIELD, "yield", 0)                                               \
   K(SUPER, "super", 0)                                               \
                                                                      \
+  /* Async await */                                                  \
+  K(ASYNC, "async", 0)                                               \
+                                                                     \
   /* Illegal token - not able to scan. */                            \
   T(ILLEGAL, "ILLEGAL", 0)                                           \
                                                                      \
   /* Scanner-internal use only. */                                   \
   T(WHITESPACE, NULL, 0)                                             \
   T(UNINITIALIZED, NULL, 0)                                          \
                                                                      \
   /* ES6 Template Literals */                                        \
   T(TEMPLATE_SPAN, NULL, 0)                                          \
   T(TEMPLATE_TAIL, NULL, 0)
@@ skipping 18 matching lines @@
 
   // Predicates
   static bool IsKeyword(Value tok) {
     return token_type[tok] == 'K';
   }
 
   static bool IsIdentifier(Value tok, LanguageMode language_mode,
                            bool is_generator) {
     switch (tok) {
       case IDENTIFIER:
+      case ASYNC:
         return true;
       case FUTURE_STRICT_RESERVED_WORD:
       case LET:
       case STATIC:
         return is_sloppy(language_mode);
       case YIELD:
         return !is_generator && is_sloppy(language_mode);
       default:
         return false;
     }
@@ skipping 103 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_TOKEN_H_