[ChromeOS] Hide 'signin-right' panel when it's empty.

So that we show Gaia horizonally center.

BUG=chromium-os:19779
TEST=Verify fix for chromium-os:19779.


Review URL: http://codereview.chromium.org/7792009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@98717 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/resources/chromeos/login/screen_gaia_signin.js

@@ -58,7 +58,10 @@ cr.define('login', function() {
     showLoadingUI_: function(show) {
       $('gaia-loading').hidden = !show;
       $('signin-frame').hidden = show;
-      $('signin-right').hidden = show;
+
+      // Sign-in right panel is hidden if all its items are hidden.
+      $('signin-right').hidden = show ||
+          ($('createAccount').hidden && $('guestSignin').hidden);
     },
 
     /**

chrome/browser/resources/chromeos/login/screen_signin.css

@@ -11,12 +11,15 @@
 }
 
 #gaia-signin {
+  -webkit-box-align: center;
+  -webkit-box-pack: center;
+  display: -webkit-box;
   height: 470px;
 }
 
 #signin-right {
-  float: right;
   font-size: 12px;
+  height: 100%;
   margin-right: 80px;
   width: 200px;
 }
@@ -30,12 +33,7 @@
 }
 
 #signin-frame {
-  bottom: 0;
   height: 100%;
-  left: 0;
-  position: absolute;
-  right: 0;
-  top: 0;
   width: 340px;
 }