[webcrypto] Refactor to use WebCryptoKeyAlgorithm create* functions.

BUG=245025

Review URL: https://codereview.chromium.org/210583003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@259143 0039d316-1c4b-4281-b951-d872f2087c98
2 files changed