Removed fixed dependencies

packages/usage/example/example.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.
 
-/// A simple web app to hand-test the usage library.
+/**
+ * A simple web app to hand-test the usage library.
+ */
 library usage_example;
 
 import 'dart:html';
 
 import 'package:usage/usage_html.dart';
 
 Analytics _analytics;
 String _lastUa;
 int _count = 0;
 
 void main() {
-  querySelector('#foo').onClick.listen((_) => _handleFoo());
-  querySelector('#bar').onClick.listen((_) => _handleBar());
-  querySelector('#page').onClick.listen((_) => _changePage());
+  querySelector('#foo').onClick.listen((_) => _handleFoo(getAnalytics()));
+  querySelector('#bar').onClick.listen((_) => _handleBar(getAnalytics()));
+  querySelector('#page').onClick.listen((_) => _changePage(getAnalytics()));
 }
 
 String _ua() => (querySelector('#ua') as InputElement).value.trim();
 
 Analytics getAnalytics() {
   if (_analytics == null || _lastUa != _ua()) {
     _lastUa = _ua();
     _analytics = new AnalyticsHtml(_lastUa, 'Test app', '1.0');
+    _analytics.optIn = true;
     _analytics.sendScreenView(window.location.pathname);
   }
 
   return _analytics;
 }
 
-void _handleFoo() {
-  Analytics analytics = getAnalytics();
+void _handleFoo(Analytics analytics) {
   analytics.sendEvent('main', 'foo');
 }
 
-void _handleBar() {
-  Analytics analytics = getAnalytics();
+void _handleBar(Analytics analytics) {
   analytics.sendEvent('main', 'bar');
 }
 
-void _changePage() {
-  Analytics analytics = getAnalytics();
+void _changePage(Analytics analytics) {
   window.history.pushState(null, 'new page', '${++_count}.html');
   analytics.sendScreenView(window.location.pathname);
 }