Previously it only supported RSA-1024/0x10001, now it also supports ECDSA-P256. This will be necessary for when KT_DEFAULT changes from KT_RSA to KT_ECDSA since FakeDtlsIdentityStore is used by many tests. BUG=webrtc:5795 R=mattdr@google.com, tommi@webrtc.org Review URL: https://codereview.webrtc.org/1965723002 . Cr-Commit-Position: refs/heads/master@{#12680}