Async constructor error message should follow V8

Fix jquery#1652
Closes jquerygh-1653

src/messages.ts

@@ -49,5 +49,6 @@ export const Messages = {
     DuplicateBinding: 'Duplicate binding %0',
     DeclarationMissingInitializer: 'Missing initializer in %0 declaration',
     LetInLexicalBinding: 'let is disallowed as a lexically bound name',
-    ForInOfLoopInitializer: '%0 loop variable declaration may not have an initializer'
+    ForInOfLoopInitializer: '%0 loop variable declaration may not have an initializer',
+    ConstructorIsAsync: 'Class constructor may not be an async method'
 };

src/parser.ts

@@ -3130,8 +3130,12 @@ export class Parser {
                     isAsync = true;
                     token = this.lookahead;
                     key = this.parseObjectPropertyKey();
-                    if (token.type === Token.Identifier && ['get', 'set', 'constructor'].indexOf(token.value) >= 0) {
-                        this.tolerateUnexpectedToken(token);
+                    if (token.type === Token.Identifier) {
+                        if (token.value === 'get' || token.value === 'set') {
+                            this.tolerateUnexpectedToken(token);
+                        } else if (token.value === 'constructor') {
+                            this.tolerateUnexpectedToken(token, Messages.ConstructorIsAsync);
+                        }
                     }
                 }
             }

test/fixtures/es2017/async/methods/invalid-async-class-constructor.failure.json

@@ -1 +1 @@
-{"index":16,"lineNumber":1,"column":17,"message":"Error: Line 1: Unexpected identifier","description":"Unexpected identifier"}
+{"index":16,"lineNumber":1,"column":17,"message":"Error: Line 1: Class constructor may not be an async method","description":"Class constructor may not be an async method"}