[webcrypto] Fix a bug with JWK private key import.

The bug would return the oldest live private key imported via JWK rather than the expected one.

BUG=378315,245025

Review URL: https://codereview.chromium.org/308523003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@275870 0039d316-1c4b-4281-b951-d872f2087c98
3 files changed