[MD Bookmarks] Add draggable sidebar.

chrome/browser/resources/md_bookmarks/toolbar.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_action_menu/cr_action_menu.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_toolbar/cr_toolbar.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button-light.html">
 <link rel="import" href="chrome://bookmarks/shared_style.html">
 <link rel="stylesheet" href="chrome://resources/css/md_colors.css">
 
 <dom-module id="bookmarks-toolbar">
   <template>
     <style include="shared-style">
       button.more-actions {
         margin: 4px;
       }
 
       button.more-vert-button div {
         border-color: white;
       }
 
       cr-toolbar {
-        --cr-toolbar-field-margin: var(--sidebar-width);
+        --cr-toolbar-field-margin:
+            calc(var(--sidebar-width) + var(--splitter-width));
         background: var(--md-toolbar-color);
       }
     </style>
     <dialog is="cr-action-menu" id="dropdown">
       <button class="dropdown-item" on-tap="onBulkEditTap_">
         $i18n{menuBulkEdit}
       </button>
       <button class="dropdown-item" on-tap="onSortTap_">
         $i18n{menuSort}
       </button>
@@ skipping 19 matching lines @@
       <button is="paper-icon-button-light" class="more-actions more-vert-button"
           on-tap="onMenuButtonOpenTap_">
         <div></div>
         <div></div>
         <div></div>
       </button>
     </cr-toolbar>
   </template>
   <script src="chrome://bookmarks/toolbar.js"></script>
 </dom-module>