DtlsIdentityStoreInterface added. New PeerConnectionFactoryInterface::CreatePeerConnection taking both service and store added (old CreatePC signature still exists).
DtlsIdentityStoreInterface added.
New PeerConnectionFactoryInterface::CreatePeerConnection taking both service and store added (old CreatePC signature still exists).

This is CL is part of an effort to land https://codereview.webrtc.org/1176383004 without breaking Chromium.
See bug for more information.

BUG=webrtc:4899
R=tommi@webrtc.org

Review URL: https://codereview.webrtc.org/1268363002 .

Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#9680}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 5b4ce3391d60229342963ef524b7c1e359e5bfc4

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