add parser parseAsync flag

pkg/analyzer/lib/src/generated/parser.dart

Index: pkg/analyzer/lib/src/generated/parser.dart
diff --git a/pkg/analyzer/lib/src/generated/parser.dart b/pkg/analyzer/lib/src/generated/parser.dart
index 33510ed07a8247196bc173ce794b9e16c4339dea..de0306f68f7c9a3cc8eca99b9598f94f1bbd2b18 100644
--- a/pkg/analyzer/lib/src/generated/parser.dart
+++ b/pkg/analyzer/lib/src/generated/parser.dart
@@ -2108,6 +2108,11 @@ class Parser {
   int _errorListenerLock = 0;
 
   /**
+   * A flag indicating whether the parser is to parse the async support.
+   */
+  bool _parseAsync = true;
+
+  /**
    * A flag indicating whether parser is to parse function bodies.
    */
   bool _parseFunctionBodies = true;
@@ -2188,6 +2193,13 @@ class Parser {
   }
 
   /**
+   * Set whether the parser is to parse the async support.
+   */
+  void set parseAsync(bool parseAsync) {
+    this._parseAsync = parseAsync;
+  }
+
+  /**
    * Set whether parser is to parse function bodies.
    */
   void set parseFunctionBodies(bool parseFunctionBodies) {
@@ -6087,6 +6099,9 @@ class Parser {
       Token star = null;
       if (_matchesString(ASYNC)) {
         keyword = getAndAdvance();
+        if (!_parseAsync) {
+          _reportErrorForToken(ParserErrorCode.ASYNC_NOT_SUPPORTED, keyword);
+        }
         if (_matches(TokenType.STAR)) {
           star = getAndAdvance();
           _inGenerator = true;
@@ -6094,6 +6109,9 @@ class Parser {
         _inAsync = true;
       } else if (_matchesString(SYNC)) {
         keyword = getAndAdvance();
+        if (!_parseAsync) {
+          _reportErrorForToken(ParserErrorCode.ASYNC_NOT_SUPPORTED, keyword);
+        }
         if (_matches(TokenType.STAR)) {
           star = getAndAdvance();
           _inGenerator = true;
@@ -9360,6 +9378,13 @@ class ParserErrorCode extends ErrorCode {
       const ParserErrorCode('ASYNC_KEYWORD_USED_AS_IDENTIFIER',
           "The keywords 'async', 'await', and 'yield' may not be used as identifiers in an asynchronous or generator function.");
 
+  /**
+   * Some environments, such as Fletch, do not support async.
+   */
+  static const CompileTimeErrorCode ASYNC_NOT_SUPPORTED =
+      const CompileTimeErrorCode('ASYNC_NOT_SUPPORTED',
+          "Async and sync are not supported in this environment.");
+
   static const ParserErrorCode BREAK_OUTSIDE_OF_LOOP = const ParserErrorCode(
       'BREAK_OUTSIDE_OF_LOOP',
       "A break statement cannot be used outside of a loop or switch statement");