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

ios/chrome/app/safe_mode_crashing_modules_config.mm

Index: ios/chrome/app/safe_mode_crashing_modules_config.mm
diff --git a/ios/chrome/app/safe_mode_crashing_modules_config.mm b/ios/chrome/app/safe_mode_crashing_modules_config.mm
index 9106d65af63356861229a1d3c0a0ae0a1569bfa7..70cabc88836d7c1b7c2c94683b1fe2c9669dd1fd 100644
--- a/ios/chrome/app/safe_mode_crashing_modules_config.mm
+++ b/ios/chrome/app/safe_mode_crashing_modules_config.mm
@@ -8,6 +8,10 @@
 #include "base/mac/foundation_util.h"
 #import "base/mac/scoped_nsobject.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 
 NSString* const kStartupCrashModulesKey = @"StartupCrashModules";