Fix two container issues for new login screen

1) We need the outer-container to be scrollable when gaia screen and
virtual keyboard are shown together, so the dark overlay ('login-shield')
should always have the same size with the larger one of
the outer-container and the scroll-container, otherwise we see areas
without overlay when scrolling up.

2) We should remember to clear contents on the small pods container
before rebuilding pods.

BUG=718156
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2916973002
Cr-Commit-Position: refs/heads/master@{#476497}

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

@@ -425,6 +425,12 @@ cr.define('cr.ui', function() {
   Oobe.setVirtualKeyboardShown = function(shown) {
     Oobe.getInstance().virtualKeyboardShown = shown;
     $('pod-row').setFocusedPodPinVisibility(!shown);
+    // The dark overlay should always have the same size with the larger one
+    // of the outer-container and the scroll-container.
+    if (shown)
+      $('login-shield').style.minHeight = $('outer-container').style.minHeight;
+    else
+      $('login-shield').style.minHeight = 'unset';
   };
 
   /**

ui/login/account_picker/md_user_pod_row.js

@@ -3122,6 +3122,7 @@ cr.define('login', function() {
       this.activatedPod_ = undefined;
       this.lastFocusedPod_ = undefined;
       this.mainPod_ = undefined;
+      this.smallPodsContainer.innerHTML = '';
 
       // Switch off animation
       Oobe.getInstance().toggleClass('flying-pods', false);