Suppress ObjC exceptions in OSXWindow::messageLoop.

Crashes have been seen inside the Cocoa-internal
NS_setFlushesWithDisplayLink function. Web searches indicate this is a
regression in macOS 11. See whether catching and ignoring these
exceptions improves stability.

Bug: angleproject:6570
Change-Id: Id0be68077163bf4e9f98189461eea016a35edd73
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3227697
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>

util/osx/OSXWindow.mm

@@ -711,6 +711,11 @@ void OSXWindow::messageLoop()
     @autoreleasepool
     {
         while (true)
+        {
+            // TODO(http://anglebug.com/6570): @try/@catch is a workaround for
+            // exceptions being thrown from Cocoa-internal function
+            // NS_setFlushesWithDisplayLink starting in macOS 11.
+            @try
             {
                 NSEvent *event = [NSApp nextEventMatchingMask:NSAnyEventMask
                                                     untilDate:[NSDate distantPast]
@@ -727,6 +732,12 @@ void OSXWindow::messageLoop()
                 }
                 [NSApp sendEvent:event];
             }
+            @catch (NSException *localException)
+            {
+                NSLog(@"*** OSXWindow discarding exception: <%@> %@", [localException name],
+                      [localException reason]);
+            }
+        }
     }
 }