Add errors per ResultPath for CertPathBuilder.

net/cert/internal/verify_certificate_chain.h

Index: net/cert/internal/verify_certificate_chain.h
diff --git a/net/cert/internal/verify_certificate_chain.h b/net/cert/internal/verify_certificate_chain.h
index 6b53d9971cc1f5b326d69e2fbaaa48f354b5f4ba..9279404e4db9e1075aa9bb473046b05bd4ca6e8d 100644
--- a/net/cert/internal/verify_certificate_chain.h
+++ b/net/cert/internal/verify_certificate_chain.h
@@ -47,8 +47,8 @@ class TrustStore;
 //      * cert_chain[N-1] must be issued by the trust anchor.
 //
 //   trust_anchor:
-//     Contains the trust anchor (root) used to verify the chain. Must be
-//     non-null.
+//     Contains the trust anchor (root) used to verify the chain. Should be
+//     non-null (null is allowed however will result in a failure).
 //
 //   signature_policy:
 //     The policy to use when verifying signatures (what hash algorithms are
@@ -97,6 +97,7 @@ extern CertErrorType kSignatureVerificationFailed;
 extern CertErrorType kValidityFailedNotAfter;
 extern CertErrorType kValidityFailedNotBefore;
 extern CertErrorType kSignatureAlgorithmsDifferentEncoding;
+extern CertErrorType kNullTrustAnchor;
 
 }  // namespace verify_certificate_chain_errors