[MD Extensions] Merge CSS into html files

chrome/browser/resources/md_extensions/item_list.html

 <link rel="import" href="chrome://resources/html/cr.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-list/iron-list.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-resizable-behavior/iron-resizable-behavior.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/neon-animation/neon-animatable-behavior.html">
 <link rel="import" href="chrome://extensions/animation_helper.html">
 <link rel="import" href="chrome://extensions/item.html">
 
 <dom-module id="extensions-item-list">
   <template>
+    <style>
+      :host {
+        @apply(--layout-vertical);
+      }
+
+      iron-list {
+        @apply(--layout-flex);
+        margin-top: 18px;
+      }
+
+      .wrapper {
+        padding: 6px;
+      }
+    </style>
     <iron-list id="list" items="[[computeShownItems_(items.*, filter)]]"
         as="item" grid>
       <template>
         <div class="wrapper">
           <extensions-item data="[[item]]" delegate="[[delegate]]"
               id="[[item.id]]" in-dev-mode="[[inDevMode]]">
           </extensions-item>
         </div>
       </template>
     </iron-list>
   </template>
-  <link rel="import" type="css" href="chrome://extensions/item_list.css">
   <script src="chrome://extensions/item_list.js"></script>
 </dom-module>