Unify iron-dropdown CSS

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 a04010cd17536ac42079476780000fd5e90f8298..7535a2e10e73ed178b40a6878543b7e610b83333 100644
--- a/chrome/browser/resources/settings/settings_shared_css.html
+++ b/chrome/browser/resources/settings/settings_shared_css.html
@@ -55,6 +55,19 @@
         outline: none;
       }
 
+      iron-dropdown .dropdown-content {
+        background-color: white;
+        box-shadow: 0 2px 6px var(--paper-grey-500);
+      }
+
+      iron-dropdown .dropdown-content > * {

[Dan Beam, 2016/07/09 00:12:05]

i think paper-item is better than "> *" here because:
a) it works even if the <paper-item> is wrapped with another tag, i.e.
<div><paper-item>
b) separators seem fairly likely in the future (and they probably shouldn't be
actionable)

[stevenjb, 2016/07/11 18:00:54]

I thought the plan was to move away from paper-item? I guess we can cross that
bridge when we get there. Changed.

+        @apply(--settings-actionable);
+      }
+
+      iron-dropdown .dropdown-content > :hover {
+        background-color: var(--settings-hover-color);
+      }
+
       span ~ a {
         -webkit-margin-start: 4px;
       }