GMC: Allow dismiss X to be focused

This CL makes the dismiss X focusable. This fixes an issue where a user
could not dismiss with the keyboard.

Bug: 1011062
Change-Id: Id35723360abd4619096f1e3a57ec0c3412af32fd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1838295Reviewed-by: Jazz Xu <jazzhsu@chromium.org>
Commit-Queue: Tommy Steimel <steimel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#702639}

chrome/browser/ui/views/global_media_controls/media_notification_container_impl.cc

@@ -78,6 +78,7 @@ MediaNotificationContainerImpl::MediaNotificationContainerImpl(
 
   auto dismiss_button = std::make_unique<DismissButton>(this);
   dismiss_button->SetPreferredSize(kDismissButtonSize);
+  dismiss_button->SetFocusBehavior(views::View::FocusBehavior::ALWAYS);
   dismiss_button->SetTooltipText(l10n_util::GetStringUTF16(
       IDS_GLOBAL_MEDIA_CONTROLS_DISMISS_ICON_TOOLTIP_TEXT));
   dismiss_button_ =