Add google analytics support

Add code to track performance metrics and events (password calculation).

externs/performance.js

@@ -0,0 +1,17 @@
+/**
+ * @return {number}
+ * @nosideeffects
+ */
+Performance.prototype.mozNow = function() {};
+
+/**
+ * @return {number}
+ * @nosideeffects
+ */
+Performance.prototype.oNow = function() {};
+
+/**
+ * @return {number}
+ * @nosideeffects
+ */
+Performance.prototype.msNow = function() {};