Explicitly set DismissButton's focus behavior

DismissButton is only used within one file and the button instance is
set to always focusable. This CL moves the focus behavior setting
directly into the class so it is clearer that this kind of button should
be always focusable.

Bug: 1001103
Change-Id: I6d2f8c59815170b19da776b029ba474fde8c03f5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2493088Reviewed-by: Tommy Steimel <steimel@chromium.org>
Commit-Queue: Wei Li <weili@chromium.org>
Cr-Commit-Position: refs/heads/master@{#820306}

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

@@ -69,6 +69,7 @@ class MediaNotificationContainerImplView::DismissButton
     views::ConfigureVectorImageButton(this);
     views::InstallFixedSizeCircleHighlightPathGenerator(
         this, kDismissButtonBackgroundRadius);
+    SetFocusBehavior(views::View::FocusBehavior::ALWAYS);
   }
 
   ~DismissButton() override = default;
@@ -126,7 +127,6 @@ MediaNotificationContainerImplView::MediaNotificationContainerImplView(
       &MediaNotificationContainerImplView::DismissNotification,
       base::Unretained(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_ =