Add parsing code for RFC 5280 PolicyConstraints.

net/cert/internal/parse_certificate.cc

Index: net/cert/internal/parse_certificate.cc
diff --git a/net/cert/internal/parse_certificate.cc b/net/cert/internal/parse_certificate.cc
index 291e91c28bfde0c58d65fb920eae072c6966b631..00e90941af04d56c682fb1f35ae8b67af00063d6 100644
--- a/net/cert/internal/parse_certificate.cc
+++ b/net/cert/internal/parse_certificate.cc
@@ -638,6 +638,7 @@ bool ParseBasicConstraints(const der::Input& basic_constraints_tlv,
     return false;
   }
   if (out->has_path_len) {
+    // TODO(eroman): Surface reason for failure if length was longer than uint8.
     if (!der::ParseUint8(encoded_path_len, &out->path_len))
       return false;
   } else {