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

ios/chrome/test/app/history_test_util.mm

Index: ios/chrome/test/app/history_test_util.mm
diff --git a/ios/chrome/test/app/history_test_util.mm b/ios/chrome/test/app/history_test_util.mm
index 1d9d8d9d1c1ca5757ceb946e4ad0a5400db7690d..500de21edffd5f76284ab3d688c3ba938db03e94 100644
--- a/ios/chrome/test/app/history_test_util.mm
+++ b/ios/chrome/test/app/history_test_util.mm
@@ -14,13 +14,17 @@
 #include "ios/chrome/browser/callback_counter.h"
 #import "ios/chrome/test/app/chrome_test_util.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace chrome_test_util {
 
 void ClearBrowsingHistory() {
   MainController* main_controller = GetMainController();
   ios::ChromeBrowserState* active_state = GetOriginalBrowserState();
   scoped_refptr<CallbackCounter> callback_counter(
-      new CallbackCounter(base::BindBlock(^{
+      new CallbackCounter(base::BindBlockArc(^{
       })));
   callback_counter->IncrementCount();
   __block bool did_complete = false;