NTP: Add transitions.

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;
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   cursor: pointer;
   text-decoration: underline;
   font-family: inherit;
 }
 
 .section {
   position: fixed;
   font-size: 12px;
 }
 
+html[anim=true][enable-section-animations=true] .section {
+  -webkit-transition: top .15s;
+}
+
 .section.disabled {
   display: none !important;
 }
 
 .section > h2 {
   font-family: Helvetica, Arial, sans-serif;
   font-size: 16px;
   font-weight: normal;
   margin: 0;
   position: relative;
 }
 
 .section:not([noexpand]) > h2 {
   cursor: pointer;
 }
 
 .section > h2 > .disclosure {
   position: absolute;
   left: -15px;
   top: 4px;
 }
 
+html[anim=true] .section > h2 > .disclosure {
+  -webkit-transition: -webkit-transform .15s;
+}
+
 .section:not(.hidden) > h2 > .disclosure {
   -webkit-transform:rotate(90deg);
 }
 
 .section > h2 .back {
   position: absolute;
   left: 0;
   top: 9px;
   width: 100%;
   height: 24px;
@@ skipping 30 matching lines @@
 }
 
 .section.hidden > h2 .settings-wrapper {
   display: none;
 }
 
 .maxiview {
   padding: 5px 0 30px;
   position: absolute;
   -webkit-mask-attachment: fixed;
+  opacity: 1;
+}
+
+.maxiview.hiding {
+  opacity: 0;
+}
+
+.maxiview.hidden {
+  display: none;
+}
+
+html[anim=true] .maxiview {
+  -webkit-transition: opacity .15s;
 }
 
 .section > .miniview {
   display: none;
-  height: 24px;
   margin: 10px 0 30px;
-  overflow: hidden;
+  white-space: nowrap;
+  overflow-x: hidden;
 }
 
 .section.hidden > * {
   display: none;
 }
 
 .section.hidden > h2,
 .section.hidden > .miniview {
   display: block;
 }
 
 .section.hidden > h2 {
   margin-right: 0;
 }
 
-.maxiview.hidden {
-  display: none;
-}
-
 .miniview > span  {
   display: inline-block;
   max-width: 114px; /* Selected so that we can fit 5 items in EN-US */
   white-space: nowrap;
   overflow: hidden;
   text-overflow: ellipsis;
   font-size: 100%;
   margin: 0 10px;
 }
 
@@ skipping 24 matching lines @@
   }
 }
 
 /* Ensure we have at least 10px horizontal marging. */
 @media (max-width: 712px) {
   #main {
     margin-left: 10px;
     margin-right: 10px;
   }
 }