move strong mode hints behind flag

pkg/analyzer/test/src/task/dart_test.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.
 
 library test.src.task.dart_test;
 
 import 'package:analyzer/src/context/cache.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/constant.dart';
 import 'package:analyzer/src/generated/element.dart';
@@ skipping 3998 matching lines @@
 void main() {
   dynamic a = [];
   a[0];
 }
 ''');
     computeResult(new LibrarySpecificUnit(source, source), STRONG_MODE_ERRORS);
     CompilationUnit unit = outputs[RESOLVED_UNIT];
 
     // validate
     _fillErrorListener(STRONG_MODE_ERRORS);
-    var errors = errorListener.errors;
-    expect(errors.length, 1);
-    expect(errors[0].errorCode.name, "dev_compiler.DynamicInvoke");
+    expect(errorListener.errors, isEmpty);
 
     List<Statement> statements = getStatementsInTopLevelFunction(unit, "main");
     ExpressionStatement statement = statements[1];
     IndexExpression idx = statement.expression;
     expect(DynamicInvoke.get(idx.target), isNotNull);
     expect(DynamicInvoke.get(idx.target), isNotNull);
     expect(DynamicInvoke.get(idx.target), isTrue);
   }
 }
 
@@ skipping 278 matching lines @@
   /**
    * Fill [errorListener] with [result] errors in the current [task].
    */
   void _fillErrorListener(ResultDescriptor<List<AnalysisError>> result) {
     List<AnalysisError> errors = task.outputs[result];
     expect(errors, isNotNull, reason: result.name);
     errorListener = new GatheringErrorListener();
     errorListener.addAll(errors);
   }
 }