[MacViews] Use NSTitledWindowMask for window modal dialogs.
[MacViews] Use NSTitledWindowMask for window modal dialogs.

-[NSApplication beginSheet:modalForWindow:...] doesn't seem to make the
sheet modal if it has NSBorderlessWindowMask.

Use NSTitledWindowMask for window modal widgets. The title is not drawn
on sheets anyway.

BUG=522359

Review URL: https://codereview.chromium.org/1291763005

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#344421}

CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend