MD Settings: Add style for disabled <select>.

chrome/browser/resources/settings/md_select_css.html

Index: chrome/browser/resources/settings/md_select_css.html
diff --git a/chrome/browser/resources/settings/md_select_css.html b/chrome/browser/resources/settings/md_select_css.html
index 708d5aabd0984e31d191bacb31bc89a7b8e64060..f528d1c8987dbed68f4b4cc8aa90f3d2f9cc1018 100644
--- a/chrome/browser/resources/settings/md_select_css.html
+++ b/chrome/browser/resources/settings/md_select_css.html
@@ -26,6 +26,14 @@
         width: 200px;
       }
 
+      /* Mirroring paper-dropdown-menu disabled style. */
+      .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%;
       }