Fix subscripting support.

build/common.gypi

 # Copyright (c) 2012 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 4015 matching lines @@
                   'STRIP_INSTALLED_PRODUCT': 'YES',
                 },
               },
               'Debug_Base': {
                 'xcode_settings': {
                   # Remove dSYM to reduce build time.
                   'DEBUG_INFORMATION_FORMAT': 'dwarf',
                 },
               },
             },
+            'xcode_settings': {
+              # It is necessary to link with the -fobjc-arc flag to use
+              # subscripting on iOS < 6.
+              'OTHER_LDFLAGS': [
+                '-fobjc-arc',
+              ],
+            },
             'conditions': [
               # TODO(justincohen): ninja builds don't support signing yet.
               ['"<(GENERATOR)"!="ninja"', {
                 'xcode_settings': {
                   'conditions': [
                     ['chromium_ios_signing', {
                       # iOS SDK wants everything for device signed.
                       'CODE_SIGN_IDENTITY[sdk=iphoneos*]': 'iPhone Developer',
                     }, {
                       'CODE_SIGNING_REQUIRED': 'NO',
@@ skipping 386 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }