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
3 files changed