pki library: Add CertIssuerSourceNSS that retrieves intermediate certs from NSS.

net/cert/internal/trust_store_nss.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_CERT_INTERNAL_TRUST_STORE_NSS_H_
 #define NET_CERT_INTERNAL_TRUST_STORE_NSS_H_
 
 #include <certt.h>
 
 #include "base/memory/ref_counted.h"
 #include "net/base/net_export.h"
 #include "net/cert/internal/trust_store.h"
 
 namespace net {
 
 // TrustStoreNSS is an implementation of TrustStore which uses NSS to find trust
 // anchors for path building.
-// TODO(mattm): also implement CertIssuerSource to return intermediates in NSS
-// DB? Or have a separate CertIssuerSourceNSS for that?  (implementing both in
-// the same class could be more efficient with some caching/etc. Need to be
-// careful about caching between different pathbuilder instances though.)
 class NET_EXPORT TrustStoreNSS : public TrustStore {
  public:
   // Creates a TrustStoreNSS which will find anchors that are trusted for
   // |trust_type|.
   explicit TrustStoreNSS(SECTrustType trust_type);
   ~TrustStoreNSS() override;
 
   // TrustStore implementation:
   void FindTrustAnchorsForCert(const scoped_refptr<ParsedCertificate>& cert,
                                TrustAnchors* matches) const override;
 
  private:
   SECTrustType trust_type_;
 
   DISALLOW_COPY_AND_ASSIGN(TrustStoreNSS);
 };
 
 }  // namespace net
 
 #endif  // NET_CERT_INTERNAL_TRUST_STORE_NSS_H_