MD Settings: settings-dropdown-menu, restore "Enter" key behavior.

chrome/browser/resources/settings/settings_shared_css.html

Index: chrome/browser/resources/settings/settings_shared_css.html
diff --git a/chrome/browser/resources/settings/settings_shared_css.html b/chrome/browser/resources/settings/settings_shared_css.html
index 859c59a3e3dbe9962badc4fd853906394d239a40..5fa45f33e7f6f5e15829ba9347598c939f8e0822 100644
--- a/chrome/browser/resources/settings/settings_shared_css.html
+++ b/chrome/browser/resources/settings/settings_shared_css.html
@@ -39,11 +39,14 @@
 
       paper-dropdown-menu .dropdown-item {
         align-items: center;

[michaelpg, 2016/07/12 23:44:22]

Have you checked if there's anything else in paper-item-shared-styles.html that
should be copied here? There's a lot of styles packed in there.

[dpapad, 2016/07/13 01:01:07]

I checked. The only thing that I see missing is the a dropdown-item[disabled]
style. But I also can't find any such cases in our UI. We tend to not show such
options at all, instead of showing them but have them disabled.

+        background: none;
+        border: none;
         color: var(--paper-grey-800);
         display: flex;
-        font-size: inherit;
+        font: inherit;
         min-height: 48px;
         padding: 0 16px;
+        width: 100%;
       }
 
       paper-dropdown-menu .dropdown-item.iron-selected {