Remove lock screen note action button tap highlight

BUG=737067

Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I29bbaeec11a59d8b1e9cab9cf584b03442ec1086
Reviewed-on: https://chromium-review.googlesource.com/580392Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Commit-Queue: Toni Barzic <tbarzic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488429}

chrome/browser/resources/chromeos/login/md_top_header_bar.css

@@ -40,6 +40,7 @@
 }
 
 .new-note-action {
+  -webkit-tap-highlight-color: transparent;
   background-color: rgba(0, 0, 0, 0.2);
   border-radius: 0 0 0 48px;
   cursor: pointer;