MD downloads: use [placeholder] instead of <label>

chrome/browser/resources/md_downloads/toolbar.html

 <link rel="import" href="chrome://resources/polymer/v1_0/polymer/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icons/iron-icons.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-item/paper-item.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-menu/paper-menu.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-menu-button/paper-menu-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button.html">
 <link rel="import" href="chrome://resources/cr_elements/v1_0/cr_button/cr_button.html">
 <link rel="import" href="chrome://resources/cr_elements/v1_0/cr_input/cr_input.html">
 <link rel="import" href="chrome://resources/html/assert.html">
 <link rel="import" href="chrome://resources/html/cr.html">
 
 <dom-module id="downloads-toolbar">
   <template>
     <div id="title">
       <h1 i18n-content="title"></h1>
     </div>
     <div id="actions">
       <cr-button class="clear-all" i18n-content="clearAll"
           on-click="onClearAllClick_"></cr-button>
       <cr-button i18n-content="openDownloadsFolder"
           on-click="onOpenDownloadsFolderClick_"></cr-button>
     </div>
     <div id="search">
       <paper-icon-button icon="search" id="search-button"
           on-click="toggleShowingSearch_"></paper-icon-button>
       <paper-input-container id="search-term" on-search="onSearchTermSearch_"
           on-keydown="onSearchTermKeydown_" hidden$="[[!showingSearch_]]"
           no-label-float>
-        <label i18n-content="search"></label>
-        <input is="iron-input" id="search-input" type="search" incremental>
+        <input is="iron-input" id="search-input" type="search"
+            i18n-values="placeholder:search" incremental>
         <paper-icon-button icon="clear" id="clear-search"
             on-click="toggleShowingSearch_"
             hidden$="[[!showingSearch_]]"></paper-icon-button>
       </paper-input-container>
       <paper-menu-button horizontal-align="right">
         <paper-icon-button icon="more-vert"
             class="dropdown-trigger"></paper-icon-button>
         <paper-menu class="dropdown-content">
           <paper-item class="clear-all" i18n-content="clearAll"
               on-click="onClearAllClick_"></paper-item>
           <paper-item i18n-content="openDownloadsFolder"
               on-click="onOpenDownloadsFolderClick_"></paper-item>
         </paper-menu>
       </paper-menu-button>
     </div>
   </template>
   <link rel="import" type="css" href="chrome://downloads/shared_style.css">
   <link rel="import" type="css" href="chrome://downloads/toolbar.css">
   <script src="chrome://downloads/toolbar.js"></script>
 </dom-module>