ChromeVox: Ensure tables in menus have 100% width.

This change updates the style for tables in the menus to ensure
they take up the most width as possible. This implicitly fixes
an issue where the 'no items' menu item was smaller than it should
have been, which was throwing off the active item highlight.

Change-Id: Iba446383302b9af217b070ae695d4701eaae7d04
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2088509
Commit-Queue: Akihiro Ota <akihiroota@chromium.org>
Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#747060}

chrome/browser/resources/chromeos/accessibility/chromevox/panel/panel.css

@@ -236,6 +236,7 @@ button {
 
 .menu {
   border-spacing: 0;
+  width: 100%;
 }
 
 .menu-item {