Make PeerConnectionClient non-singleton. Ownership of EglBase is moved to PeerConnectionClient. BUG=webrtc:8135 Review-Url: https://codereview.webrtc.org/3007893002 Cr-Original-Commit-Position: refs/heads/master@{#19634} Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc Cr-Mirrored-Commit: 85d7650ab6a84477e807d458ea835154cf5138da