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

ui/views/bubble/bubble_frame_view.cc

Index: ui/views/bubble/bubble_frame_view.cc
diff --git a/ui/views/bubble/bubble_frame_view.cc b/ui/views/bubble/bubble_frame_view.cc
index 079300c90f2f8a8bad141d0cacb92f7ac96379d2..6a19a176b35c5845d52bf832ab5d46538837fa5a 100644
--- a/ui/views/bubble/bubble_frame_view.cc
+++ b/ui/views/bubble/bubble_frame_view.cc
@@ -133,6 +133,14 @@ Button* BubbleFrameView::CreateCloseButton(ButtonListener* listener) {
   }
   close_button->SetTooltipText(l10n_util::GetStringUTF16(IDS_APP_CLOSE));
   close_button->SizeToPreferredSize();
+
+  // Remove the close button from tab traversal on all platforms. It defaults to

[msw, 2017/07/12 17:20:25]

nit: remove the "It defaults to" sentence

[tapted, 2017/07/12 23:49:10]

Done.

+  // FocusBehavior::ACCESSIBLE_ONLY which (apart from on Mac) only affects
+  // buttons in AccessiblePaneViews (which the close button is not). Note this
+  // does not affect screen readers' ability to focus the element. Keyboard

[msw, 2017/07/12 17:20:25]

nit: s/element/close button/

[tapted, 2017/07/12 23:49:10]

Done.

+  // access to this element when not using a screen reader is done via the ESC

[msw, 2017/07/12 17:20:25]

nit: s/this element/the close button/

[tapted, 2017/07/12 23:49:10]

Done.

+  // key handler in DialogClientView.
+  close_button->SetFocusBehavior(View::FocusBehavior::NEVER);
   return close_button;
 }