MD User Manager: "Select an account" should just be a label not a menu entry

chrome/browser/resources/md_user_manager/create_profile.html

 <link rel="import" href="chrome://md-user-manager/import_supervised_user.html">
 <link rel="import" href="chrome://md-user-manager/profile_browser_proxy.html">
 <link rel="import" href="chrome://md-user-manager/shared_styles.html">
 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/html/action_link.html">
 <link rel="import" href="chrome://resources/html/cr.html">
 <link rel="import" href="chrome://resources/html/i18n_behavior.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/html/util.html">
 <link rel="import" href="chrome://resources/html/web_ui_listener_behavior.html">
@@ skipping 53 matching lines @@
 
       #title-bar {
         border-bottom: 1px solid rgba(0, 0, 0, .12);
         font-size: 16px;
         font-weight: 500;
         padding: 104px 0 16px;
       }
 
       #nameInput,
       paper-dropdown-menu {
-        --paper-input-container-color: var(--primary-text-color);
-        --paper-input-container-focus-color: var(--google-blue-500);
         --paper-input-container-input: {
           font-size: inherit;
         };
+        --paper-input-container-label: {
+          font-size: inherit;
+        };
+        --paper-input-container-underline-focus: var(--google-blue-500);
       }
 
       #nameInput {
         margin-bottom: 24px;
         margin-top: 32px;
         width: 300px;
       }
 
       #icons {
         display: flex;
@@ skipping 105 matching lines @@
       </div>
       <paper-checkbox checked="{{isSupervised_}}">
         $i18n{manageProfilesSupervisedSignedInLabel}
       </paper-checkbox>
       <div id="supervised-user-container">
         <div id="learn-more" >
           <a is="action-link" on-tap="onLearnMoreTap_">$i18n{learnMore}</a>
         <div>
         <template is="dom-if" if="[[isSupervised_]]">
           <template is="dom-if" if="[[isSignedIn_(signedInUsers_)]]">
-            <paper-dropdown-menu no-label-float>
+            <paper-dropdown-menu label="$i18n{selectAnAccount}" no-label-float>
               <paper-listbox class="dropdown-content"
                   selected="{{signedInUserIndex_}}"
                   attr-for-selected="data-user-index">
-                <paper-item data-user-index$="[[sentinelSignedInUserIndex_]]">
-                  $i18n{selectAnAccount}
-                </paper-item>
                 <template is="dom-repeat" items="[[signedInUsers_]]">
                   <paper-item data-user-index$="[[index]]">
                     [[item.username]]
                   </paper-item>
                 </template>
               </paper-listbox>
             </paper-dropdown-menu>
             <a id="import-user" is="action-link" on-tap="onImportUserTap_"
                 hidden="[[isImportUserLinkHidden_(createInProgress_,
                                                   signedInUserIndex_)]]">
@@ skipping 15 matching lines @@
         <paper-button id="save" class="action primary" on-tap="onSaveTap_"
             disabled="[[isSaveDisabled_(createInProgress_, profileName_)]]">
           $i18n{createProfileConfirm}
         </paper-button>
       </div>
       <import-supervised-user id="importUserPopup"></import-supervised-user>
     </div>
   </template>
   <script src="chrome://md-user-manager/create_profile.js"></script>
 </dom-module>