move strong mode hints behind flag

pkg/analyzer/test/src/task/strong/strong_test_helper.dart

 // Copyright (c) 2015, 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.
 
 // TODO(jmesserly): this file needs to be refactored, it's a port from
 // package:dev_compiler's tests
 library test.src.task.strong.strong_test_helper;
 
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
@@ skipping 57 matching lines @@
       new MockDartSdk(mockSdkSources, reportMissing: true).resolver,
       uriResolver
     ]);
 
     // Run the checker on /main.dart.
     Source mainSource = uriResolver.resolveAbsolute(new Uri.file('/main.dart'));
     var initialLibrary =
         context.resolveCompilationUnit2(mainSource, mainSource);
 
     var collector = new _ErrorCollector();
-    var checker =
-        new CodeChecker(new TypeRules(context.typeProvider), collector);
+    var checker = new CodeChecker(
+        new TypeRules(context.typeProvider), collector,
+        hints: true);
 
     // Extract expectations from the comments in the test files, and
     // check that all errors we emit are included in the expected map.
     var allLibraries = reachableLibraries(initialLibrary.element.library);
     for (var lib in allLibraries) {
       for (var unit in lib.units) {
         var errors = <AnalysisError>[];
         collector.errors = errors;
 
         var source = unit.source;
@@ skipping 400 matching lines @@
   if (levelName == 'warning') return _MAGENTA_COLOR;
   if (levelName == 'info') return _CYAN_COLOR;
   return null;
 }
 
 const String _RED_COLOR = '\u001b[31m';
 const String _MAGENTA_COLOR = '\u001b[35m';
 const String _CYAN_COLOR = '\u001b[36m';
 const String GREEN_COLOR = '\u001b[32m';
 const String NO_COLOR = '\u001b[0m';