[ObjC ARC] Converts ios/chrome/browser/ui/util:util to ARC.

ios/chrome/browser/ui/util/unicode_util.mm

 // Copyright 2015 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/browser/ui/util/unicode_util.h"
 
 #include "base/logging.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace unicode_util {
 namespace {
 // Character ranges for characters with R or AL bidirectionality.
 // http://www.ietf.org/rfc/rfc3454.txt
 const NSUInteger kRTLRangeCount = 34;
 unichar kRTLUnicodeRanges[kRTLRangeCount][2] = {
     {0x05BE, 0x05BE}, {0x05C0, 0x05C0}, {0x05C3, 0x05C3}, {0x05D0, 0x05EA},
     {0x05F0, 0x05F4}, {0x061B, 0x061B}, {0x061F, 0x061F}, {0x0621, 0x063A},
     {0x0640, 0x064A}, {0x066D, 0x066F}, {0x0671, 0x06D5}, {0x06DD, 0x06DD},
     {0x06E5, 0x06E6}, {0x06FA, 0x06FE}, {0x0700, 0x070D}, {0x0710, 0x0710},
@@ skipping 84 matching lines @@
     else if (c < 0x0100)
       zero_prefix = @"00";
     else if (c < 0x1000)
       zero_prefix = @"0";
     [unicode_string appendFormat:@"\\u%@%x", zero_prefix, c];
   }
   return unicode_string;
 }
 
 }  // namespace unicode_util