Fix FTAViewController incorrectly calling [UIApplication openURL] on a non-main thread (#461)

Author: dconeybe

testing/sample_framework/src/ios/ios_app_framework.mm

@@ -90,10 +90,11 @@ - (void)viewDidLoad {
     delete[] argv[0];
     argv[0] = nullptr;
     [NSThread sleepForTimeInterval:kGameLoopSecondsToPauseBeforeQuitting];
-    [UIApplication.sharedApplication openURL:[NSURL URLWithString:kGameLoopCompleteUrlScheme]
-                                     options:[NSDictionary dictionary]
-                           completionHandler:nil];
-
+    dispatch_async(dispatch_get_main_queue(), ^{
+      [UIApplication.sharedApplication openURL:[NSURL URLWithString:kGameLoopCompleteUrlScheme]
+                                       options:[NSDictionary dictionary]
+                             completionHandler:nil];
+    });
   });
 }