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

ios/chrome/test/base/scoped_block_swizzler.mm

Index: ios/chrome/test/base/scoped_block_swizzler.mm
diff --git a/ios/chrome/test/base/scoped_block_swizzler.mm b/ios/chrome/test/base/scoped_block_swizzler.mm
index 7ce6f6a723a6367f3e0fd7fb6a0499c807a79c42..2f2bee398a660bcbd819e5ce97dc94795bd740dc 100644
--- a/ios/chrome/test/base/scoped_block_swizzler.mm
+++ b/ios/chrome/test/base/scoped_block_swizzler.mm
@@ -6,6 +6,10 @@
 
 #include "base/logging.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 ScopedBlockSwizzler::ScopedBlockSwizzler(Class target, SEL selector, id block) {
   method_ = class_getInstanceMethod(target, selector);
   if (!method_) {