MD Bookmarks: Validate URL input when editing a bookmark

chrome/browser/resources/md_bookmarks/edit_dialog.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/html/assert.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_dialog/cr_dialog.html">
 <link rel="import" href="chrome://resources/cr_elements/shared_style_css.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-input/paper-input.html">
 
 <dom-module id="bookmarks-edit-dialog">
   <template>
     <style include="cr-shared-style"></style>
     <dialog is="cr-dialog" id="dialog">
       <div class="title">[[getDialogTitle_(isFolder_)]]</div>
       <div class="body">
         <paper-input always-float-label id="name"
             label="$i18n{editDialogNameInput}"
             value="{{titleValue_}}"
             autofocus>
         </paper-input>
         <paper-input always-float-label id="url"
+            type="url"
             label="$i18n{editDialogUrlInput}"
+            error-message="$i18n{editDialogInvalidUrl}"
             value="{{urlValue_}}"
-            hidden$="[[isFolder_]]">
+            hidden$="[[isFolder_]]"
+            required>
         </paper-input>
       </div>
       <div class="button-container">
         <paper-button class="cancel-button" on-tap="onCancelButtonTap_">
           $i18n{cancelEdit}
         </paper-button>
         <paper-button id="saveButton" class="action-button"
             on-tap="onSaveButtonTap_">
           $i18n{saveEdit}
         </paper-button>
       </div>
     </dialog>
   </template>
   <script src="chrome://bookmarks/edit_dialog.js"></script>
 </dom-module>