MD Bookmarks: Support policies for disabling bookmark editing

ui/webui/resources/cr_elements/cr_toolbar/cr_toolbar_selection_overlay.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-button/paper-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button-light.html">
 
 <dom-module id="cr-toolbar-selection-overlay">
   <template>
     <style>
       :host {
         -webkit-padding-start: var(--cr-toolbar-field-margin, 0);
         display: flex;
         height: 56px;
       }
 
       #overlay-content {
         align-items: center;
         display: flex;
         flex: 1;
         margin: 0 auto;
         max-width: var(--selection-overlay-max-width, initial);
         padding: 0 var(--selection-overlay-padding, 24px);
       }
 
       paper-button {
         font-weight: 500;
       }
 
+      paper-button[disabled] {
+        background: transparent;
+        color: inherit;
+        opacity: 0.7;
+      }
+
       #number-selected {
         flex: 1;
       }
 
       button {
         -webkit-margin-end: 24px;
         -webkit-margin-start: 2px;
         height: 36px;
         width: 36px;
       }
 
       button iron-icon {
         height: 20px;
         width: 20px;
       }
     </style>
     <div id="overlay-content">
       <button is="paper-icon-button-light"
           on-tap="onClearSelectionTap_"
           title="[[cancelLabel]]">
         <iron-icon icon="cr:clear"></iron-icon>
       </button>
       <div id="number-selected">[[selectionLabel]]</div>
       <paper-button on-tap="onClearSelectionTap_">
         [[cancelLabel]]
       </paper-button>
-      <paper-button id="delete" on-tap="onDeleteTap_">
+      <paper-button id="delete" on-tap="onDeleteTap_"
+          disabled="[[deleteDisabled]]">
         [[deleteLabel]]
       </paper-button>
     </div>
   </template>
   <script src="cr_toolbar_selection_overlay.js"></script>
 </dom-module>