WebUI: Fix md-select disabled look after adding left/right padding.

ui/webui/resources/html/md_select_css.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-styles/color.html">
 
 <dom-module id="md-select">
   <template>
     <style>
       .md-select,
       .md-select-underline {
         --md-side-padding: 12px;
       }
@@ skipping 16 matching lines @@
         font-family: inherit;
         font-size: inherit;
         outline: none;
         padding-bottom: 4px;
         padding-top: 3px;
         width: calc(var(--md-select-width, 200px) + 2 * var(--md-side-padding));
       }
 
       /* Mirroring paper-dropdown-menu disabled style. */
       .md-select[disabled] {
-        border-bottom: 1px dashed var(--secondary-text-color);
-        color: var(--secondary-text-color);
-        opacity: 0.65;
         pointer-events: none;
       }
 
+      .md-select[disabled],
+      .md-select[disabled] + .md-select-underline {
+        color: var(--secondary-text-color);
+        opacity: 0.65;
+      }
+
       :host-context([dir=rtl]) .md-select {
         background-position-x: calc(var(--md-side-padding) + 3%);
       }
 
       /* Persistent underline */
       .md-select-underline {
         -webkit-margin-end: 0;
         -webkit-margin-start: var(--md-side-padding);
         border-top: 1px solid var(--paper-grey-300);
         display: block;
@@ skipping 17 matching lines @@
       .md-select-underline::after {
         position: relative;
         top: -1px;
       }
 
       .md-select:focus + .md-select-underline::after {
         transform: scale3d(1, 1, 1);
         transition: transform 200ms ease-out;
       }
 
+      .md-select[disabled] + .md-select-underline {
+        border-top: 1px dashed var(--secondary-text-color);
+      }
+
       .md-select-wrapper {
         display: inline-block;
         max-width: 100%;
       }
     </style>
   </template>
 </dom-module>