Automatically set correct Observatory analytics version

runtime/observatory/lib/src/app/analytics.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.
 
 part of app;
 
 class Analytics {
   static final _UA = 'UA-26406144-17';
   static final _name = 'Observatory';
-  static final _version = '1.11';
+  static final _version = const String.fromEnvironment('OBS_VER');
   static final _googleAnalytics = new AnalyticsHtml(_UA, _name, _version);
 
   static initialize() {
     // We only send screen views. This is allowed without user permission.
     // Note, before flipping this to be true we need a UI to allow users to
     // control this.
     _googleAnalytics.optIn = false;
   }
 
   /// Called whenever an Observatory page is viewed.
   static Future reportPageView(Uri uri) {
     // Only report analytics when running in JavaScript.
     if (Utils.runningInJavaScript()) {
       // The screen name is the uri's path. e.g. inspect, profile.
       final screenName = uri.path;
       return _googleAnalytics.sendScreenView(screenName);
     } else {
       return new Future.value(null);
     }
   }
 }