[MD History] Focus search field on load.

This CL fixes an issue where the search field was not focused on load
after a CSS change. This seemed to happen because the transition caused
a frame of 'visibility: hidden' to race with the toolbar focus() call.

Bug: 857370
Cq-Include-Trybots: luci.chromium.try:closure_compilation
Change-Id: Id4ac3b15e1f1a886b6fb1c3af4512a878fb87150
Reviewed-on: https://chromium-review.googlesource.com/1122027Reviewed-by: Alan Cutter <alancutter@chromium.org>
Commit-Queue: calamity <calamity@chromium.org>
Cr-Commit-Position: refs/heads/master@{#572522}

ui/webui/resources/cr_elements/cr_toolbar/cr_toolbar.html

@@ -16,7 +16,6 @@
         color: #fff;
         display: flex;
         height: var(--cr-toolbar-height);
-        transition: visibility var(--cr-toolbar-overlay-animation-duration);
       }
 
       h1 {
@@ -64,6 +63,7 @@
       }
 
       :host([has-overlay]) {
+        transition: visibility var(--cr-toolbar-overlay-animation-duration);
         visibility: hidden;
       }