Add support for MD2, MD4, and MD5 to SignatureAlgorithm.

(At a parsing level it is useful to recognize these for error handling,
even if in practice they aren't used when verifying signatures.)

Review-Url: https://codereview.chromium.org/2728953003
Cr-Commit-Position: refs/heads/master@{#455350}
(cherry picked from commit 37e84a0d658536248f4a4372551c36db2e614c1f)

BUG=690821

Review-Url: https://codereview.chromium.org/2750703002 .
Cr-Commit-Position: refs/branch-heads/3029@{#165}
Cr-Branched-From: 939b32ee5ba05c396eef3fd992822fcca9a2e262-refs/heads/master@{#454471}
11 files changed