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}
BUG=webrtc:5876 R=deadbeef@webrtc.org, solenberg@webrtc.org Review-Url: https://codereview.webrtc.org/3004723002 . Cr-Commit-Position: refs/heads/master@{#19639}