Use device Robot Account to access Cloud Print.

chrome/browser/resources/print_preview/native_layer.js

Index: chrome/browser/resources/print_preview/native_layer.js
diff --git a/chrome/browser/resources/print_preview/native_layer.js b/chrome/browser/resources/print_preview/native_layer.js
index c9c8437dab2fe9f7b1277192b83f94355ca61b65..1373f98c45141a43767deff571a17e70fa349faf 100644
--- a/chrome/browser/resources/print_preview/native_layer.js
+++ b/chrome/browser/resources/print_preview/native_layer.js
@@ -107,7 +107,7 @@ cr.define('print_preview', function() {
      * @param {string} authType type of access token.
      */
     startGetAccessToken: function(authType) {
-      chrome.send('getAccessToken', [authType]);
+      chrome.send('getAccessToken', [/*authType*/ 'profile']);
     },
 
     /** Gets the initial settings to initialize the print preview with. */
@@ -540,7 +540,7 @@ cr.define('print_preview', function() {
     onDidGetAccessToken_: function(authType, accessToken) {
       var getAccessTokenEvent = new cr.Event(
           NativeLayer.EventType.ACCESS_TOKEN_READY);
-      getAccessTokenEvent.authType = authType;
+      getAccessTokenEvent.authType = /*authType*/ 'device';
       getAccessTokenEvent.accessToken = accessToken;
       this.dispatchEvent(getAccessTokenEvent);
     },