[ObjC ARC] Converts ios/chrome/app:unit_tests to ARC.

ios/chrome/app/deferred_initialization_runner_unittest.mm

Index: ios/chrome/app/deferred_initialization_runner_unittest.mm
diff --git a/ios/chrome/app/deferred_initialization_runner_unittest.mm b/ios/chrome/app/deferred_initialization_runner_unittest.mm
index dd242beade1f29fa4602c4c8292baaf2579863dd..6ed95f99e6a39af6546f8775fe52890e3c927914 100644
--- a/ios/chrome/app/deferred_initialization_runner_unittest.mm
+++ b/ios/chrome/app/deferred_initialization_runner_unittest.mm
@@ -8,6 +8,10 @@
 #include "base/time/time.h"
 #include "testing/platform_test.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 TEST(DeferredInitializationRunnerTest, TestSharedInstance) {
   EXPECT_TRUE([DeferredInitializationRunner sharedInstance]);
   // Cancelling a non-existing block does nothing.