Remove the BubbleFrameView close button from tab traversal on all platforms.

ui/views/bubble/bubble_frame_view.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/views/bubble/bubble_frame_view.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "build/build_config.h"
@@ skipping 115 matching lines @@
                            *rb->GetImageNamed(IDR_CLOSE_DIALOG).ToImageSkia());
     close_button->SetImage(
         CustomButton::STATE_HOVERED,
         *rb->GetImageNamed(IDR_CLOSE_DIALOG_H).ToImageSkia());
     close_button->SetImage(
         CustomButton::STATE_PRESSED,
         *rb->GetImageNamed(IDR_CLOSE_DIALOG_P).ToImageSkia());
   }
   close_button->SetTooltipText(l10n_util::GetStringUTF16(IDS_APP_CLOSE));
   close_button->SizeToPreferredSize();
+
+  // Remove the close button from tab traversal on all platforms. Note this does
+  // not affect screen readers' ability to focus the close button. Keyboard
+  // access to the close button when not using a screen reader is done via the
+  // ESC key handler in DialogClientView.
+  close_button->SetFocusBehavior(View::FocusBehavior::NEVER);
   return close_button;
 }
 
 gfx::Rect BubbleFrameView::GetBoundsForClientView() const {
   gfx::Rect client_bounds = GetContentsBounds();
   client_bounds.Inset(GetInsets());
   if (footnote_container_) {
     client_bounds.set_height(client_bounds.height() -
                              footnote_container_->height());
   }
@@ skipping 418 matching lines @@
 
   DialogDelegate* dialog_delegate =
       GetWidget()->widget_delegate()->AsDialogDelegate();
   if (dialog_delegate && dialog_delegate->ShouldSnapFrameWidth())
     size.set_width(LayoutProvider::Get()->GetSnappedDialogWidth(size.width()));
 
   return size;
 }
 
 }  // namespace views