Create ECPrivateKey from secret

- Derive ECPrivateKey from secret deterministically using
  EC_KEY_derive_from_secret
- Will be used for VapidKeyManager to generate a ECPrivateKey from
  256-bit secret from Chrome Sync, as illustrated in
  https://crrev.com/c/1848171

Bug: 1010968
Change-Id: Id2445ff802e9598ad3b454dc42972a6812713885
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1844961
Commit-Queue: Alex Chau <[email protected]>
Reviewed-by: David Benjamin <[email protected]>
Reviewed-by: Richard Knoll <[email protected]>
Cr-Commit-Position: refs/heads/master@{#705661}
3 files changed