Window selector close button missing accessible name

This is split out from the CL to test all widgets and views for nameless
focusable objects. See crrev.com/c/951933.

Bug: 819350
Change-Id: I4435ed2c1c6fcb7148abc2a15570d07c2dca292a
Reviewed-on: https://chromium-review.googlesource.com/961090Reviewed-by: James Cook <jamescook@chromium.org>
Commit-Queue: Aaron Leventhal <aleventhal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542928}

ash/wm/overview/window_selector_item.cc

@@ -44,6 +44,7 @@
 #include "ui/gfx/image/image_skia_operations.h"
 #include "ui/gfx/paint_vector_icon.h"
 #include "ui/gfx/transform_util.h"
+#include "ui/strings/grit/ui_strings.h"
 #include "ui/views/animation/flood_fill_ink_drop_ripple.h"
 #include "ui/views/animation/ink_drop_impl.h"
 #include "ui/views/animation/ink_drop_mask.h"
@@ -279,6 +280,7 @@ WindowSelectorItem::OverviewCloseButton::OverviewCloseButton(
                     views::ImageButton::ALIGN_MIDDLE);
   const int length = IsNewOverviewUi() ? kHeaderHeightDp : kOldHeaderHeightDp;
   SetMinimumImageSize(gfx::Size(length, length));
+  SetAccessibleName(l10n_util::GetStringUTF16(IDS_APP_ACCNAME_CLOSE));
 }
 
 WindowSelectorItem::OverviewCloseButton::~OverviewCloseButton() = default;