chrome/settings: Shorten strings in appearance, downloads, date&time.

chrome/browser/resources/settings/appearance_page/appearance_page.html

 <link rel="import" href="chrome://resources/polymer/v1_0/polymer/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-material/paper-material.html">
 <link rel="import" href="chrome://md-settings/checkbox/checkbox.html">
 
 <dom-module id="cr-settings-appearance-page">
   <link rel="import" type="css"
       href="chrome://md-settings/settings_page/settings_page.css">
   <link rel="import" type="css"
       href="chrome://md-settings/appearance_page/appearance_page.css">
   <link rel="import" type="css" href="chrome://resources/css/widgets.css">
   <link rel="import" href="chrome://resources/html/action_link.html">
   <template>
     <paper-material>
       <div id="action-container">
         <cr-button i18n-content="setWallpaper"></cr-button>
         <cr-button i18n-content="getThemes"></cr-button>
         <cr-button i18n-content="resetToDefaultTheme" disabled></cr-button>
       </div>
       <hr>
-      <cr-settings-checkbox
-          pref="{{prefs.browser.show_home_button}}"
-          i18n-values="label:appearanceShowHomeButtonLabel">
+      <cr-settings-checkbox pref="{{prefs.browser.show_home_button}}"
+          i18n-values="label:showHomeButton">
       </cr-settings-checkbox>
       <div id="change-home-page-section" hidden$="{{!prefs.browser.show_home_button.value}}">
         <div id="change-home-page-section-container">
           <span id="home-page-ntp" i18n-content="homePageNtp"></span>
           <span id="home-page-url"></span>
           <a is="action-link" id="change-home-page"
               i18n-content="changeHomePage">
           </a>
       </div>
     </div>
-      <cr-settings-checkbox
-          pref="{{prefs.bookmark_bar.show_on_all_tabs}}"
-          i18n-values="label:appearanceShowBookmarksBarLabel">
+      <cr-settings-checkbox pref="{{prefs.bookmark_bar.show_on_all_tabs}}"
+          i18n-values="label:showBookmarksBar">
       </cr-settings-checkbox>
     </paper-material>
   </template>
   <script src="appearance_page.js"></script>
 </dom-module>