Better error message for missing async with await

pkg/analysis_server/test/services/correction/fix_test.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library test.services.correction.fix;
 
 import 'dart:async';
 
 import 'package:analysis_server/plugin/edit/fix/fix_core.dart';
 import 'package:analysis_server/plugin/edit/fix/fix_dart.dart';
@@ skipping 454 matching lines @@
     // No fix for ";".
     {
       AnalysisError error = errors[0];
       expect(error.message, "Expected to find ';'.");
       List<Fix> fixes = await _computeFixes(error);
       expect(fixes, isEmpty);
     }
     // Has fix for "await".
     {
       AnalysisError error = errors[1];
-      expect(error.message, startsWith("Undefined name 'await'."));
+      expect(error.message, startsWith("Undefined name 'await' in function"));
       List<Fix> fixes = await _computeFixes(error);
       // has exactly one fix
       expect(fixes, hasLength(1));
       Fix fix = fixes[0];
       expect(fix.kind, DartFixKind.ADD_ASYNC);
       // apply to "file"
       List<SourceFileEdit> fileEdits = fix.change.edits;
       expect(fileEdits, hasLength(1));
       resultCode = SourceEdit.applySequence(testCode, fileEdits[0].edits);
       // verify
@@ skipping 5162 matching lines @@
 
   @override
   final CompilationUnit unit;
 
   @override
   final AnalysisError error;
 
   _DartFixContextImpl(this.resourceProvider, this.getTopLevelDeclarations,
       this.analysisContext, this.unit, this.error);
 }