Added chrome switch that lets tests override URL path, moved GAIA auth extension from CrOS

chrome/browser/resources/gaia_auth/success.js

Index: chrome/browser/resources/gaia_auth/success.js
diff --git a/chrome/browser/resources/gaia_auth/success.js b/chrome/browser/resources/gaia_auth/success.js
new file mode 100644
index 0000000000000000000000000000000000000000..f3a0efcdb4046e0895ce3de037714c0193006d13
--- /dev/null
+++ b/chrome/browser/resources/gaia_auth/success.js
@@ -0,0 +1,14 @@
+function load() {
+  console.log('### Authenticator success page loaded.');
+
+  var params = getUrlSearchParams(location.search);
+  var msg = {
+    'method': 'confirmLogin',
+    'attemptToken': params['attemptToken']
+  };
+  window.parent.postMessage(msg,
+          'chrome-extension://mfffpogegjflfpflabcdkioaeobkgjik/main.html');
+}
+
+document.addEventListener('DOMContentLoaded', load);
+