NTP: Don't show any sections or layout until we receive mv and apps.

chrome/browser/resources/new_new_tab.css

 html {
   /* This is needed because of chrome://theme/css/new_tab.css */
   height: 100%;
 }
 
 body {
   margin: 0;
   height: 100%;
   overflow: auto;
   -webkit-user-select: none;
   cursor: default;
 }
 
 html[mode=app-launcher] {
   height: auto;
 }
 
 #main {
   -webkit-box-sizing: border-box;
   -webkit-transition: width .15s;
   margin: 0 auto;
   min-height: 100%;
 }
 
+body.loading #main {
+  /* We start out hidden to prevent glitchiness as the app and most visited
+  data flows in. */
+  visibility: hidden;
+}
+
 #main,
 .section,
 .maxiview {
   width: 920px;
 }
 
 html[dir=rtl] #main {
   background-position-x: 100%;
 }
 
@@ skipping 366 matching lines @@
   }
 }
 
 /* Ensure we have at least 10px horizontal marging. */
 @media (max-width: 712px) {
   #main {
     margin-left: 10px;
     margin-right: 10px;
   }
 }