CrOS Shelf: Enable arrow key traversal in all cases

This makes arrow traversal behavior consistent with what the launcher
does, allowing left/right and up/down arrow traversal of the shelf
regardless of the shelf's orientation. Tab/right/down all have the same
effect, and shift-tab/left/up all have the same effect.

Bug: 888637
Change-Id: Ife5aaed19388ee6fde1293e1760e87cc6e22eb5e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1535462Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Alex Newcomer <newcomer@chromium.org>
Commit-Queue: Manu Cornet <manucornet@chromium.org>
Cr-Commit-Position: refs/heads/master@{#644153}

ash/shelf/shelf_view.cc

@@ -2205,11 +2205,6 @@ void ShelfView::OnShelfAlignmentChanged(aura::Window* root_window) {
   if (app_list_button)
     app_list_button->SchedulePaint();
 
-  if (GetFocusManager()) {
-    GetFocusManager()->set_arrow_key_traversal_enabled_for_widget(
-        !shelf_->IsHorizontalAlignment());
-  }
-
   AnnounceShelfAlignment();
 }
 

ash/shelf/shelf_widget.cc

@@ -373,6 +373,7 @@ ShelfWidget::~ShelfWidget() {
 void ShelfWidget::Initialize() {
   // Sets initial session state to make sure the UI is properly shown.
   OnSessionStateChanged(Shell::Get()->session_controller()->GetSessionState());
+  GetFocusManager()->set_arrow_key_traversal_enabled_for_widget(true);
 }
 
 void ShelfWidget::Shutdown() {