Move optional.h to webrtc/api/
We use Optional in our public API, so its header should be in
webrtc/api/.
BUG=webrtc:8205
Review-Url: https://codereview.webrtc.org/3011943002
Cr-Commit-Position: refs/heads/master@{#19693}
diff --git a/webrtc/modules/audio_coding/acm2/acm_receiver.h b/webrtc/modules/audio_coding/acm2/acm_receiver.h
index 5acb013..ebeecec 100644
--- a/webrtc/modules/audio_coding/acm2/acm_receiver.h
+++ b/webrtc/modules/audio_coding/acm2/acm_receiver.h
@@ -17,6 +17,7 @@
#include <vector>
#include "webrtc/api/array_view.h"
+#include "webrtc/api/optional.h"
#include "webrtc/common_audio/vad/include/webrtc_vad.h"
#include "webrtc/modules/audio_coding/acm2/acm_resampler.h"
#include "webrtc/modules/audio_coding/acm2/call_statistics.h"
@@ -24,7 +25,6 @@
#include "webrtc/modules/audio_coding/neteq/include/neteq.h"
#include "webrtc/modules/include/module_common_types.h"
#include "webrtc/rtc_base/criticalsection.h"
-#include "webrtc/rtc_base/optional.h"
#include "webrtc/rtc_base/thread_annotations.h"
#include "webrtc/typedefs.h"