[webauthn] Return SecurityError when providing an invalid icon URL

Webauthn allows invalid icon URLs to pass through. This refactors
CredentialsContainer to use KURL::IsNull() instead of KURL::IsEmpty()
to check for empty URLs. IsEmpty() returns `true` for malformed
URLs.

Bug: 901589
Change-Id: I66fee9a5451f74b5873a3925b916cd9d95fb17ae
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1586335
Commit-Queue: Nina Satragno <nsatragno@chromium.org>
Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Reviewed-by: Kim Paulhamus <kpaulhamus@chromium.org>
Cr-Commit-Position: refs/heads/master@{#656808}
5 files changed