MD Settings: Content Settings: Support guest mode.

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/i18n_behavior.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">
@@ skipping 405 matching lines @@
           <site-data-details-subpage page-title="{{pageTitle}}">
           </site-data-details-subpage>
         </settings-subpage>
       </template>
       <template is="dom-if" route-path="/content/protectedContent" no-search>
         <settings-subpage page-title="$i18n{siteSettingsProtectedContent}">
           <div class="settings-box first">
             <settings-toggle-button class="start"
                 pref="{{prefs.webkit.webprefs.encrypted_media_enabled}}"
                 label="[[getProtectedContentLabel_(
-                    prefs.webkit.webprefs.encrypted_media_enabled.value)]]">
+                    prefs.webkit.webprefs.encrypted_media_enabled.value)]]"
+                disabled$="[[isGuest_]]">

[tommycli, 2017/02/14 00:28:39]

The existing usages of isGuest_ in the code specify that the control is entirely
gone (dom-ifed out). In these cases UI specified it should be just disabled?

[stevenjb, 2017/02/14 00:49:23]

This is consistent with current Settings. I stuck with this model because:
a) Exceptions can still be added
b) It may help explain to the user why it doesn't work. Ideally at some point we
could add a policy like icon here with an explanatory tooltip.

             </settings-toggle-button>
           </div>
 <if expr="chromeos or is_win">
           <div class="settings-box first two-line">
             $i18n{siteSettingsProtectedContentIdentifiersExplanation}
           </div>
           <div class="settings-box first">
             <settings-toggle-button class="start"
                 pref="{{prefs.settings.privacy.drm_enabled}}"
                 label="[[getProtectedContentIdentifiersLabel_(
-                    prefs.settings.privacy.drm_enabled.value)]]">
+                    prefs.settings.privacy.drm_enabled.value)]]"
+                disabled$="[[isGuest_]]">
             </settings-toggle-button>
           </div>
 </if>
 <if expr="chromeos">
           <template is="dom-if"
               if="[[prefs.settings.privacy.drm_enabled.value]]">
             <category-setting-exceptions
                 category="{{ContentSettingsTypes.PROTECTED_CONTENT}}">
             </category-setting-exceptions>
           </template>
 </if>
         </settings-subpage>
       </template>
     </settings-animated-pages>
   </template>
   <script src="privacy_page.js"></script>
 </dom-module>