Use javascript strict mode throughout a number of net-internals files.

chrome/browser/resources/net_internals/util.js

Index: chrome/browser/resources/net_internals/util.js
===================================================================
--- chrome/browser/resources/net_internals/util.js	(revision 95298)
+++ chrome/browser/resources/net_internals/util.js	(working copy)
@@ -143,6 +143,18 @@
 }
 
 /**
+ * Helper to make sure singleton classes are not instantiated more than once.
+ */
+function assertFirstConstructorCall(ctor) {
+  // This is the variable which is set by cr.addSingletonGetter().
+  if (ctor.hasCreateFirstInstance_) {
+    throw Error('The class ' + ctor.name + ' is a singleton, and should ' +
+                'only be accessed using ' + ctor.name + '.getInstance().');
+  }
+  ctor.hasCreateFirstInstance_ = true;
+}
+
+/**
  * TablePrinter is a helper to format a table as ascii art or an HTML table.
  *
  * Usage: call addRow() and addCell() repeatedly to specify the data.