iOS: Set enable_protobuf=1 by default.

webrtc/build/common.gypi

 # Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 # This file contains common settings for building WebRTC components.
 
@@ skipping 130 matching lines @@
         # http://code.google.com/p/webrtc/issues/detail?id=163
         'clang_use_chrome_plugins%': 0,
 
         'include_pulse_audio%': 1,
         'include_internal_audio_device%': 1,
         'include_tests%': 1,
         'restrict_webrtc_logging%': 0,
       }],
       ['OS=="ios"', {
         'build_libjpeg%': 0,
-        'enable_protobuf%': 0,
       }],
       ['target_arch=="arm" or target_arch=="arm64"', {
         'prefer_fixed_point%': 1,
       }],
       ['(target_arch=="arm" and (arm_neon==1 or arm_neon_optional==1)) or target_arch=="arm64"', {
         'build_with_neon%': 1,
       }],
       ['OS!="ios" and (target_arch!="arm" or arm_version>=7) and target_arch!="mips64el"', {
         'rtc_use_openmax_dl%': 1,
       }, {
@@ skipping 278 matching lines @@
           # of a more specific macro.
           'defines': [
             'WEBRTC_POSIX',
           ],
         }],
       ],
     },
   }, # target_defaults
 }