Make sure UI methods get called on the main thread

webrtc/examples/objc/AppRTCMobile/mac/APPRTCViewController.m

Index: webrtc/examples/objc/AppRTCMobile/mac/APPRTCViewController.m
diff --git a/webrtc/examples/objc/AppRTCMobile/mac/APPRTCViewController.m b/webrtc/examples/objc/AppRTCMobile/mac/APPRTCViewController.m
index c23e0d59cd234e962fe00c1fa6dfc86789f6fd9b..d6aa71038ac146e354b76ceb5c24460d96fa098a 100644
--- a/webrtc/examples/objc/AppRTCMobile/mac/APPRTCViewController.m
+++ b/webrtc/examples/objc/AppRTCMobile/mac/APPRTCViewController.m
@@ -63,10 +63,12 @@ @implementation APPRTCMainView  {
 
 
 - (void)displayLogMessage:(NSString *)message {
-  _logView.string =
-      [NSString stringWithFormat:@"%@%@\n", _logView.string, message];
-  NSRange range = NSMakeRange(_logView.string.length, 0);
-  [_logView scrollRangeToVisible:range];
+  dispatch_async(dispatch_get_main_queue(), ^{
+    _logView.string =
+        [NSString stringWithFormat:@"%@%@\n", _logView.string, message];
+    NSRange range = NSMakeRange(_logView.string.length, 0);
+    [_logView scrollRangeToVisible:range];
+  });
 }
 
 #pragma mark - Private
@@ -413,9 +415,11 @@ - (APPRTCMainView*)mainView {
 }
 
 - (void)showAlertWithMessage:(NSString*)message {
-  NSAlert* alert = [[NSAlert alloc] init];
-  [alert setMessageText:message];
-  [alert runModal];
+  dispatch_async(dispatch_get_main_queue(), ^{
+    NSAlert* alert = [[NSAlert alloc] init];
+    [alert setMessageText:message];
+    [alert runModal];
+  });
 }
 
 - (void)resetUI {