CREDENTIAL: Implement 'SiteBoundCredential'.
This patch shims 'SiteBoundCredential' between 'Credential' and
'{Password,Federated}Credential'. I don't see any need to push this noop
up the stack, however, so it does not introduce a similar concept at
the platform layer, nor does //content need to learn about this
indirection.
As a drive-by, this patch adds some IDL tests for 'CredentialsContainer'
since it was adding IDL tests for 'PasswordCredential' and
'FederatedCredential' anyway.
BUG=
602980
Committed:
https://crrev.com/be6cc81fc74f63c8e134525bbf15ea966c8403d5
Cr-Commit-Position: refs/heads/master@{#389475}