Add NetLog support to UDP sockets.

chrome/browser/resources/net_internals/source_tracker.js

Index: chrome/browser/resources/net_internals/source_tracker.js
===================================================================
--- chrome/browser/resources/net_internals/source_tracker.js	(revision 105148)
+++ chrome/browser/resources/net_internals/source_tracker.js	(working copy)
@@ -77,6 +77,17 @@
   return this.sourceEntries_[id];
 };
 
+/**
+ * Returns the description of the specified SourceEntry, or an empty string if
+ * it doesn't exist.
+ */
+SourceTracker.prototype.getDescription = function(id) {
+  var entry = this.getSourceEntry(id);
+  if (entry)
+    return entry.getDescription();
+  return '';
+};
+
 SourceTracker.prototype.onReceivedPassiveLogEntries = function(logEntries) {
   // Due to an expected race condition, it is possible to receive actively
   // captured log entries before the passively logged entries are received.