MD Settings: make custom UIs look "actionable"

chrome/browser/resources/settings/settings_shared_css.html

 <link rel="import" href="chrome://resources/cr_elements/shared_style_css.html">
 <link rel="import" href="/settings_root_css.html">
 
 <!-- Common styles for Material Design settings. -->
 <dom-module id="settings-shared">
   <template>
     <style include="cr-shared-style">
       h2 {
         align-items: center;
         display: flex;
@@ skipping 212 matching lines @@
         display: block;
       }
 
       /*
        * A row with two lines of text. Often the lower line will be .secondary.
        */
       .settings-box.two-line {
         min-height: 56px;
       }
 
+      [actionable] {
+        @apply(--settings-actionable);
+      }
+
       /* The lower line of text in a .settings-box.two-line. */
       .settings-box .secondary {
         @apply(--settings-secondary);
       }
 
       /* The middle part (horizontally) of a row. */
       .settings-box .middle {
         -webkit-margin-start: 16px;
         align-items: center;
         flex: auto;
@@ skipping 46 matching lines @@
 
       .favicon-image {
         background-repeat: no-repeat;
         background-size: contain;
         height: 16px;
         width: 16px;
       }
     </style>
   </template>
 </dom-module>