add parser parseAsync flag

pkg/analyzer/lib/src/context/context.dart

Index: pkg/analyzer/lib/src/context/context.dart
diff --git a/pkg/analyzer/lib/src/context/context.dart b/pkg/analyzer/lib/src/context/context.dart
index ac3ace6b60aea7cddb20eba996750446286be647..2ea723187c52c9e667970f060fc0e9de5f264c14 100644
--- a/pkg/analyzer/lib/src/context/context.dart
+++ b/pkg/analyzer/lib/src/context/context.dart
@@ -253,6 +253,7 @@ class AnalysisContextImpl implements InternalAnalysisContext {
         this._options.enableStrictCallChecks !=
             options.enableStrictCallChecks ||
         this._options.enableGenericMethods != options.enableGenericMethods ||
+        this._options.enableAsync != options.enableAsync ||
         this._options.enableSuperMixins != options.enableSuperMixins;
     int cacheSize = options.cacheSize;
     if (this._options.cacheSize != cacheSize) {
@@ -266,6 +267,7 @@ class AnalysisContextImpl implements InternalAnalysisContext {
     this._options.enableGenericMethods = options.enableGenericMethods;
     this._options.enableAssertMessage = options.enableAssertMessage;
     this._options.enableStrictCallChecks = options.enableStrictCallChecks;
+    this._options.enableAsync = options.enableAsync;
     this._options.enableSuperMixins = options.enableSuperMixins;
     this._options.hint = options.hint;
     this._options.incremental = options.incremental;