[refactor] Split up SourceTracker into SourceTracker + EventsTracker.

chrome/browser/resources/net_internals/source_entry.js

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 var SourceEntry = (function() {
   'use strict';
 
   /**
    * A SourceEntry gathers all log entries with the same source.
    *
@@ skipping 90 matching lines @@
           break;
         case LogSourceType.HTTP_PIPELINED_CONNECTION:
           if (e.params.host_and_port)
             this.description_ = e.params.host_and_port;
           break;
         case LogSourceType.SOCKET:
           // Use description of parent source, if any.
           if (e.params.source_dependency != undefined) {
             var parentId = e.params.source_dependency.id;
             this.description_ =
-                g_browser.sourceTracker.getDescription(parentId);
+                SourceTracker.getInstance().getDescription(parentId);
           }
           break;
         case LogSourceType.UDP_SOCKET:
           if (e.params.address != undefined) {
             this.description_ = e.params.address;
             // If the parent of |this| is a HOST_RESOLVER_IMPL_JOB, use
             // '<DNS Server IP> [<host we're resolving>]'.
             if (this.entries_[0].type == LogEventType.SOCKET_ALIVE &&
                 this.entries_[0].params.source_dependency != undefined) {
               var parentId = this.entries_[0].params.source_dependency.id;
-              var parent = g_browser.sourceTracker.getSourceEntry(parentId);
+              var parent = SourceTracker.getInstance().getSourceEntry(parentId);
               if (parent &&
                   parent.getSourceType() ==
                       LogSourceType.HOST_RESOLVER_IMPL_JOB &&
                   parent.getDescription().length > 0) {
                 this.description_ += ' [' + parent.getDescription() + ']';
               }
             }
           }
           break;
         case LogSourceType.ASYNC_HOST_RESOLVER_REQUEST:
@@ skipping 157 matching lines @@
      * Prints descriptive text about |entries_| to a new node added to the end
      * of |parent|.
      */
     printAsText: function(parent) {
       printLogEntriesAsText(this.entries_, parent);
     }
   };
 
   return SourceEntry;
 })();