MD Settings: Add description for Protected Content

chrome/browser/resources/settings/privacy_page/privacy_page.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/cr_elements/policy/cr_policy_vars_css.html">
 <link rel="import" href="chrome://resources/html/web_ui_listener_behavior.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/iron-flex-layout-classes.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/neon-animation/neon-animatable.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">
 <link rel="import" href="../clear_browsing_data_dialog/clear_browsing_data_dialog.html">
 <link rel="import" href="../controls/settings_toggle_button.html">
 <link rel="import" href="../lifetime_browser_proxy.html">
@@ skipping 423 matching lines @@
               on-tap="onRemoveAllCookiesFromSite_">
             $i18n{siteSettingsCookieRemoveAll}
           </paper-button>
           <site-data-details-subpage page-title="{{pageTitle}}">
           </site-data-details-subpage>
         </settings-subpage>
       </template>
 <if expr="chromeos or is_win">
       <template is="dom-if" route-path="/content/protectedContent" no-search>
         <settings-subpage page-title="$i18n{siteSettingsProtectedContent}">
+          <div class="settings-box first two-line">
+            $i18n{siteSettingsProtectedContentExplanation}
+          </div>
           <div class="settings-box first">
             <settings-toggle-button class="start"
                 pref="{{prefs.settings.privacy.drm_enabled}}"
                 label="$i18n{siteSettingsProtectedContentEnable}">
             </settings-toggle-button>
           </div>
         </settings-subpage>
       </template>
 </if>
     </settings-animated-pages>
   </template>
   <script src="privacy_page.js"></script>
 </dom-module>