iSAC: Make separate AudioEncoder and AudioDecoder objects

webrtc/modules/audio_coding/audio_coding.gypi

 # Copyright (c) 2015 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.
 
 {
   'includes': [
     '../../build/common.gypi',
     'codecs/interfaces.gypi',
     'codecs/cng/cng.gypi',
     'codecs/g711/g711.gypi',
     'codecs/g722/g722.gypi',
     'codecs/ilbc/ilbc.gypi',
     'codecs/isac/isac.gypi',
+    'codecs/isac/isac_common.gypi',
     'codecs/isac/isacfix.gypi',
     'codecs/pcm16b/pcm16b.gypi',
     'codecs/red/red.gypi',
     'main/audio_coding_module.gypi',
     'neteq/neteq.gypi',
   ],
   'conditions': [
     ['include_opus==1', {
       'includes': ['codecs/opus/opus.gypi',],
     }],
   ],
 }