Move optional.h to webrtc/api/

webrtc/common_audio/BUILD.gn

 # Copyright (c) 2014 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.
 
 import("//build/config/arm.gni")
 import("../webrtc.gni")
@@ skipping 45 matching lines @@
     "wav_file.h",
     "wav_header.cc",
     "wav_header.h",
     "window_generator.cc",
     "window_generator.h",
   ]
 
   deps = [
     ":sinc_resampler",
     "..:webrtc_common",
+    "../api:optional",
     "../rtc_base:gtest_prod",
     "../rtc_base:rtc_base_approved",
     "../system_wrappers",
   ]
   public_deps = [
     ":common_audio_c",
   ]
 
   defines = []
   if (rtc_use_openmax_dl) {
@@ skipping 333 matching lines @@
       "//testing/gtest",
     ]
 
     if (is_android) {
       deps += [ "//testing/android/native_test:native_test_support" ]
 
       shard_timeout = 900
     }
   }
 }