Tests for CryptohomeKeyDelegate: algs, ext errors

Add more browser tests for the CryptohomeKeyDelegate implementation,
for these scenarios:

* a key that supports two algorithms simultaneously;
* another signature algorithm (PKCS #1 v1.5 SHA-1) besides PKCS #1 v1.5
  SHA-256;
* an unsupported signature algorithm;
* the extension removing the key that it reported before;
* the extension failing the signature operation.

Bug: 826417
Change-Id: Ie298c506a26debfcead64fb8209a2174fedc52b2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1706440
Commit-Queue: Maksim Ivanov <emaxx@chromium.org>
Reviewed-by: Pavol Marko <pmarko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#682298}