Add kAccessibilityFocusFallsbackToWidget property

ui/views/widget/widget.cc

Index: ui/views/widget/widget.cc
diff --git a/ui/views/widget/widget.cc b/ui/views/widget/widget.cc
index b14dce1f8f4eeb69271a7dee479816ac5e22ae10..ffc6acec0384389a73157cf0d1cd3735551ffdf0 100644
--- a/ui/views/widget/widget.cc
+++ b/ui/views/widget/widget.cc
@@ -331,6 +331,7 @@ void Widget::Init(const InitParams& in_params) {
   ownership_ = params.ownership;
   native_widget_ = CreateNativeWidget(params, this)->AsNativeWidgetPrivate();
   root_view_.reset(CreateRootView());
+  root_view_->SetFocusBehavior(View::FocusBehavior::ACCESSIBLE_ONLY);

[sky, 2016/11/30 16:26:04]

Can you clarify why you want this? The change here means *every* widget will
have it's root view accessible. Many widgets are not activatable, or things you
wouldn't want to have focus (say tooltips for example). Many bubbles also don't
want focus. In other words this doesn't seem like the right change, but I could
be misunderstanding what this does and why you want it.

[yawano, 2016/12/01 00:24:23]

Added comment.

   default_theme_provider_.reset(new ui::DefaultThemeProvider);
   if (params.type == InitParams::TYPE_MENU) {
     is_mouse_button_pressed_ =