Fix a warning

pkg/analyzer/test/generated/strong_mode_test.dart

 // Copyright (c) 2016, 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 analyzer.test.generated.strong_mode_test;
 
 import 'dart:async';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/standard_resolution_map.dart';
@@ skipping 1087 matching lines @@
     var a1 = new A.fromMap({'hello' : 3});
     var a2 = new A.fromList([3]);
     var a3 = new A.fromT(3);
     var a4 = new A.fromB(new B(3));
 }
    ''';
     CompilationUnit unit = await resolveSource(code);
     Element elementA = AstFinder.getClass(unit, "A").element;
     List<Statement> statements =
         AstFinder.getStatementsInTopLevelFunction(unit, "test");
-    DartType check(int i) {
+    void check(int i) {
       VariableDeclarationStatement stmt = statements[i];
       VariableDeclaration decl = stmt.variables.variables[0];
       Expression init = decl.initializer;
       _isInstantiationOf(_hasElement(elementA))([_isInt])(init.staticType);
     }
 
     for (var i = 0; i < 5; i++) check(i);
   }
 
   test_inferConstructor_unknownTypeLowerBound() async {
@@ skipping 2802 matching lines @@
   var v = x;
   v; // marker
 }
 int x = 3;
 ''';
     CompilationUnit unit = await resolveSource(code);
     assertPropagatedAssignedType(code, unit, typeProvider.intType, null);
     assertTypeOfMarkedExpression(code, unit, typeProvider.intType, null);
   }
 }