Introduce CertVerifierProc to handle system cert validation.

Introduce a CertVerifierProc  to handle system cert validation.

In preparation for moving certificate path building and
verification out of X509Certificate, introduce a
CertVerifierProc that can be used by the
MultiThreadedCertVerifier to verify certificates using the
underlying system store.

Unit tests previously coded against X509Certificate are now
coded against the CertVerifierProc, as future CLs will shift
verification into this interface.

This was originally reviewed as http://codereview.chromium.org/9584041/ and
http://codereview.chromium.org/9553014/ , and has been
combined in order to preserve SVN history.

BUG=114343
TEST=net_unittests
R=wtc
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=128150

[Ryan Sleevi, 2012-03-22 01:16:31]

wtc: TBR; you already reviewed these - this just copies the patches into my svn
directory so that I can preserve the metadata for the unittests.

[wtc, 2012-03-22 01:43:47]

LGTM.

Please add R=...,BUG=114343,TEST=... to the CL's description.

In the CL's description, it would be nice to name the helper
class and stub class rather than using the vague terms.