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

ios/chrome/app/safe_mode_crashing_modules_config.mm

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ios/chrome/app/safe_mode_crashing_modules_config.h"
 
 #include "base/logging.h"
 #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";
 NSString* const kModuleFriendlyNameKey = @"ModuleFriendlyName";
 
 }  // namespace
 
-@interface SafeModeCrashingModulesConfig () {
-  base::scoped_nsobject<NSDictionary> _configuration;
+@implementation SafeModeCrashingModulesConfig {
+  NSDictionary* _configuration;
 }
-@end
-
-@implementation SafeModeCrashingModulesConfig
 
 + (SafeModeCrashingModulesConfig*)sharedInstance {
   static SafeModeCrashingModulesConfig* instance =
       [[SafeModeCrashingModulesConfig alloc] init];
   return instance;
 }
 
 - (instancetype)init {
   self = [super init];
   if (self) {
     NSString* configPath =
         [[NSBundle mainBundle] pathForResource:@"SafeModeCrashingModules"
                                         ofType:@"plist"];
-    _configuration.reset(
-        [[NSDictionary alloc] initWithContentsOfFile:configPath]);
+    _configuration = [[NSDictionary alloc] initWithContentsOfFile:configPath];
   }
   return self;
 }
 
 - (NSString*)startupCrashModuleFriendlyName:(NSString*)modulePath {
   NSDictionary* modules = base::mac::ObjCCastStrict<NSDictionary>(
       [_configuration objectForKey:kStartupCrashModulesKey]);
   NSDictionary* module =
       base::mac::ObjCCastStrict<NSDictionary>(modules[modulePath]);
   return base::mac::ObjCCast<NSString>(module[kModuleFriendlyNameKey]);
 }
 
 @end