bug#30699: 26.0.91; buffer contents flicker on macOS frames when frames are resized

[Eli Zaretskii]

> From: Aaron Jensen <aaronjensen@gmail.com>
> Date: Tue, 20 Mar 2018 14:50:14 -0700
> Cc: Eli Zaretskii <eliz@gnu.org>, 30699@debbugs.gnu.org
> 
> I've been having crashes on master today. Here's the dump (I didn't
> have lldb attached at the time). Thread 5 is what pointed me to this:
> 
> 3   com.apple.SkyLight                0x00007fff594c6b44
> CGSUpdateManager::enable_update(unsigned long long) + 320

That's an internal NS function, isn't it?

AFAIU, the important part is this:

> 10  org.gnu.Emacs                     0x00000001000bb44e handle_sigsegv + 168
> 11  libsystem_platform.dylib          0x00007fff5f781f5a _sigtramp + 26
> 12  ???                               000000000000000000 0 + 0
> 13  com.apple.AppKit                  0x00007fff351c0d9d
> -[NSApplication run] + 812
> 14  org.gnu.Emacs                     0x00000001001795b2 -[EmacsApp run] + 373
> 15  org.gnu.Emacs                     0x000000010018434f ns_read_socket + 536
> 16  org.gnu.Emacs                     0x00000001000ac523 gobble_input + 234

Why does [EmacsApp run] trigger a SIGSEGV?