Context MenuItem Touch Feedback

Modify Menu.jr to also respond to touch events. Provide visual touch feedback based on mouse hover.

TEST=Manual testing of Bookmark Manager
BUG=398404

Review URL: https://codereview.chromium.org/584553005

Cr-Commit-Position: refs/heads/master@{#295779}

ui/webui/resources/css/menu.css

@@ -59,11 +59,7 @@ menu > [hidden] {
   display: none;
 }
 
-menu > :not(hr)[selected] {
-  background-color: rgba(0, 0, 0, .06);
-}
-
-menu > :not(hr)[selected]:active {
+menu > :not(hr):-webkit-any([selected], :active) {
   background-color: rgba(0, 0, 0, .06);
 }