MD Settings: allow changing to GTK+ theme on Linux

chrome/browser/resources/settings/appearance_page/appearance_page.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/polymer/v1_0/iron-flex-layout/classes/iron-flex-layout.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="/appearance_page/appearance_browser_proxy.html">
 <link rel="import" href="/controls/controlled_radio_button.html">
 <link rel="import" href="/controls/settings_dropdown_menu.html">
 <link rel="import" href="/controls/settings_input.html">
 <link rel="import" href="/controls/settings_radio_group.html">
 <link rel="import" href="/route.html">
 <link rel="import" href="/settings_page/settings_animated_pages.html">
 <link rel="import" href="/settings_page/settings_subpage.html">
 <link rel="import" href="/settings_shared_css.html">
 <link rel="import" href="appearance_fonts_page.html">
 
 <dom-module id="settings-appearance-page">
   <template>
     <style include="settings-shared">
       :host {
         --paper-input-container-label: {
           font-size: inherit;
           font-weight: inherit;
         };
       }
+
+      .secondary-button ~ .secondary-button {
+        -webkit-margin-start: 12px;
+      }
     </style>
     <settings-animated-pages id="pages" section="appearance">
       <neon-animatable route-path="default">
 <if expr="chromeos">
         <div class="settings-box first two-line" id="wallpaperButton"
             on-tap="openWallpaperManager_" actionable
             hidden="[[!pageVisibility.setWallpaper]]">
           <div class="start">
             $i18n{setWallpaper}
             <div class="secondary">$i18n{openWallpaperApp}</div>
           </div>
           <button class="icon-external" is="paper-icon-button-light"></button>
         </div>
         <div class="settings-box two-line"
             hidden="[[!pageVisibility.setTheme]]" actionable>
 </if>
 <if expr="not chromeos">
         <div class="settings-box two-line first"
             hidden="[[!pageVisibility.setTheme]]" actionable>
 </if>
           <div class="start two-line" on-tap="openThemesGallery_">
             <div class="flex">
-              <div>$i18n{theme}</div>
+              <div>$i18n{themes}</div>
               <div class="secondary">[[themeSublabel_]]</div>
             </div>
             <button class="icon-external" is="paper-icon-button-light"></button>
           </div>
-          <template is="dom-if" if="[[allowResetTheme_]]">
+<if expr="not is_linux or chromeos">
+          <template is="dom-if" if="[[prefs.extensions.theme.id.value]]">
             <div class="secondary-action">
-              <paper-button id="resetTheme" on-tap="resetTheme_"
+              <paper-button id="useDefault" on-tap="onUseDefaultTap_"
                   class="secondary-button">
                 $i18n{resetToDefaultTheme}
               </paper-button>
             </div>
           </template>
+</if>
+<if expr="is_linux and not chromeos">
+          <div class="secondary-action">
+            <template is="dom-if" if="[[showUseClassic_(
+                prefs.extensions.theme.id.value, useSystemTheme_)]]" restamp>
+              <paper-button id="useDefault" on-tap="onUseDefaultTap_"
+                  class="secondary-button">
+                $i18n{useClassicTheme}
+              </paper-button>
+            </template>
+            <template is="dom-if" if="[[showUseSystem_(
+                prefs.extensions.theme.id.value, useSystemTheme_)]]" restamp>
+              <paper-button id="useSystem" on-tap="onUseSystemTap_"
+                  class="secondary-button">
+                $i18n{useSystemTheme}
+              </paper-button>
+            </template>
+          </div>
+</if>
         </div>
         <div class="settings-box"
             hidden="[[!pageVisibility.homeButton]]">
           <settings-checkbox class="start" label="$i18n{showHomeButton}"
               sub-label="[[getShowHomeSubLabel_(prefs.homepage_is_newtabpage.value, prefs.homepage.value)]]"
               pref="{{prefs.browser.show_home_button}}">
           </settings-checkbox>
         </div>
         <template is="dom-if" if="[[prefs.browser.show_home_button.value]]">
           <div class="list-frame"
@@ skipping 59 matching lines @@
             associated-control="[[$$('#customize-fonts-subpage-trigger')]]"
             page-title="$i18n{customizeFonts}">
           <settings-appearance-fonts-page prefs="{{prefs}}">
           </settings-appearance-fonts-page>
         </settings-subpage>
       </template>
     </settings-animated-pages>
   </template>
   <script src="appearance_page.js"></script>
 </dom-module>