ChromeOS Gaia: send message 'handshake' to Gaia to establish connection channel

chrome/browser/resources/gaia_auth_host/authenticator.js

Index: chrome/browser/resources/gaia_auth_host/authenticator.js
diff --git a/chrome/browser/resources/gaia_auth_host/authenticator.js b/chrome/browser/resources/gaia_auth_host/authenticator.js
index 5bcca328842925ab240634774b315213561f4d44..c40ce80991d1c1d35328851ecceaae0cbdf0a59c 100644
--- a/chrome/browser/resources/gaia_auth_host/authenticator.js
+++ b/chrome/browser/resources/gaia_auth_host/authenticator.js
@@ -332,7 +332,10 @@ cr.define('cr.login', function() {
     // Posts a message to IdP pages to initiate communication.
     var currentUrl = this.webview_.src;
     if (currentUrl.lastIndexOf(this.idpOrigin_) == 0) {
-      this.webview_.contentWindow.postMessage({}, currentUrl);
+      var msg = {
+        'method': 'handshake'
+      };
+      this.webview_.contentWindow.postMessage(msg, currentUrl);
     }
   };