Switch MD Settings to paper-dropdown-menu-light

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_vars_css.html">
 
 <!-- Common styles for Material Design settings. -->
 <dom-module id="settings-shared">
   <template>
     <style include="cr-shared-style">
       /* Use <h2> as the "sub-header" mentioned in the UX design docs. */
       h2 {
         align-items: center;
@@ skipping 17 matching lines @@
       }
 
       paper-button[toggles][active] {
         background-color: var(--paper-grey-300);
       }
 
       paper-toggle-button {
         @apply(--settings-actionable);
       }
 
-      paper-dropdown-menu {
+      paper-dropdown-menu-light {
         --iron-icon-fill-color: var(--paper-grey-600);
         --paper-font-subhead: {
           font-size: inherit;
         };
-        --paper-input-container-underline: {
-          background: var(--paper-grey-300);
+        --paper-dropdown-menu-input: {
+          border-bottom-color: var(--paper-grey-300);
         };
+        /* Offsets the input's border-bottom. */
+        top: 1px;
       }
 
       iron-dropdown .dropdown-content,
-      paper-dropdown-menu paper-listbox {
+      paper-dropdown-menu-light paper-listbox {
         min-width: 128px;
         padding: 8px 0;
       }
 
       iron-dropdown .dropdown-item,
-      paper-dropdown-menu .dropdown-item,
+      paper-dropdown-menu-light .dropdown-item,
       cr-shared-menu .dropdown-item {
         align-items: center;
         background: none;
         border: none;
         color: var(--paper-grey-800);
         display: flex;
         font: inherit;
         min-height: 32px;
         padding: 0 24px;
         text-align: start;
         width: 100%;
       }
 
-      paper-dropdown-menu .dropdown-item.iron-selected {
+      paper-dropdown-menu-light .dropdown-item.iron-selected {
         font-weight: bold;
       }
 
       iron-dropdown .dropdown-item:focus,
-      paper-dropdown-menu .dropdown-item:focus {
+      paper-dropdown-menu-light .dropdown-item:focus {
         @apply(--cr-selectable-focus);
       }
 
       iron-dropdown .dropdown-content {
         background-color: white;
         box-shadow: 0 2px 6px var(--paper-grey-500);
       }
 
       iron-dropdown .dropdown-content .dropdown-item:not([disabled]),
       cr-shared-menu .dropdown-item:not([disabled]),
@@ skipping 297 matching lines @@
       /* Turns the arrow direction downwards, when the bubble is placed above
        * the anchor element */
       .search-bubble-innards.above::after {
         -webkit-transform: rotate(-135deg);
         bottom: -5px;
         top: auto;
       }
     </style>
   </template>
 </dom-module>