MD Settings: Add style for disabled <select>.

chrome/browser/resources/settings/md_select_css.html

 <link rel="import" href="/settings_vars_css.html">
 
 <dom-module id="md-select">
   <template>
     <style>
       .md-select {
         --md-arrow-width: 0.9em;
         -webkit-appearance: none;
         /* Ensure that the text does not overlap with the down arrow. */
         -webkit-padding-end: calc(var(--md-arrow-width) * 1.8);
         background: url(images/arrow_down.svg) 97% center no-repeat;
         background-size: var(--md-arrow-width);
         border-bottom: 1px solid var(--paper-grey-300);
         border-left: none;
         /* Override Mac's default border-radius */
         border-radius: 0;
         border-right: none;
         border-top: none;
         color: var(--primary-text-color);
         cursor: pointer;
         font-family: inherit;
         font-size: inherit;
         outline: none;
         padding-bottom: 3px;
         padding-top: 3px;
         width: 200px;
       }
 
+      /* Mirroring paper-dropdown-menu disabled style */

[dschuyler, 2016/10/11 00:12:41]

nit: period at the end
style. */

[dpapad, 2016/10/11 00:31:48]

Done.

+      .md-select[disabled] {
+        border-bottom: 1px dashed var(--secondary-text-color);
+        color: var(--secondary-text-color);
+        opacity: 0.33;
+        pointer-events: none;
+      }
+
       :host-context([dir=rtl]) .md-select {
         background-position-x: 3%;
       }
 
       .md-select-underline {
         border-top: 2px solid var(--google-blue-500);
         display: block;
         position: relative;
         top: -1px;
         transform: scale3d(0, 1, 1);
         transition: transform 200ms ease-in;
         width: 100%;
       }
 
       .md-select:focus + .md-select-underline {
         transform: scale3d(1, 1, 1);
         transition: transform 200ms ease-out;
       }
 
       .md-select-wrapper {
         display: inline-block;
       }
     </style>
   </template>
 </dom-module>