Version: r387838 (52.0.2711.0)
OS: Linux

What steps will reproduce the problem?
(1) Chrome menu -> More tools -> Add to desktop.
(2) Click / drag the page behind the dialog.

What is the expected output?
Add to Desktop dialog is modal; clicking on page behind has no effect.

(Actually, prior to r387104 it just dismissed the dialog, but I think having it be modal makes more sense.)

What do you see instead?
In a Debug build or Release-with-DCHECKs, opening the window DCHECK-fails:
[11759:11759:0420/164350:FATAL:constrained_window_views.cc(163)] Check failed: ui::MODAL_TYPE_NONE != dialog->GetModalType() (0 vs. 0)
#0 0x7f2b20cda94e base::debug::StackTrace::StackTrace()
#1 0x7f2b20cf9eeb logging::LogMessage::~LogMessage()
#2 0x7f2b22242b0a constrained_window::CreateBrowserModalDialogViews()
#3 0x7f2b221846f7 BookmarkAppConfirmationView::CreateAndShow()
#4 0x7f2b21a8d9c1 extensions::BookmarkAppHelper::OnIconsDownloaded()

In a Release build, the page behind is interactive (the dialog is non-modal).

BookmarkAppConfirmationView needs to override WidgetDelegate::GetModalType to return MODAL_TYPE_WINDOW.

This was broken in r387104 (https://codereview.chromium.org/1878963003) which rewrote the bookmark dialog with BookmarkAppConfirmationView.