All strong mode cleaning of dart2js.

pkg/compiler/lib/src/helpers/helpers.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 for debugging helpers. The unittest analyze_unused_test checks that
 /// the helper are not used in production code.
 
 library dart2js.helpers;
 
 import '../common.dart';
@@ skipping 76 matching lines @@
   return _reportHere;
 }
 
 /// Implementation of [reportHere]
 _reportHere(DiagnosticReporter reporter, Spannable node, String debugMessage) {
   reporter
       .reportInfo(node, MessageKind.GENERIC, {'text': 'HERE: $debugMessage'});
 }
 
 /// Set of tracked objects used by [track] and [ifTracked].
-var _trackedObjects = new Set();
+var _trackedObjects = new Set<Object>();
 
 /// Global default value for the `printTrace` option of [track] and [ifTracked].
 bool trackWithTrace = false;
 
 /// If [doTrack] is `true`, add [object] to the set of tracked objects.
 ///
 /// If tracked, [message] is printed along the hash code and toString of
 /// [object]. If [printTrace] is `true` a trace printed additionally.
 /// If [printTrace] is `null`, [trackWithTrace] determines whether a trace is
 /// printed.
@@ skipping 26 matching lines @@
       if (printTrace) {
         trace(msg);
       } else {
         debugPrint(msg);
       }
     }
     return true;
   }
   return false;
 }