Account for the OS returning an empty certificate chain.

net/cert/cert_verify_proc.h

 // Copyright (c) 2012 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_CERT_VERIFY_PROC_H_
 #define NET_CERT_CERT_VERIFY_PROC_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 58 matching lines @@
  protected:
   CertVerifyProc();
   virtual ~CertVerifyProc();
 
  private:
   friend class base::RefCountedThreadSafe<CertVerifyProc>;
   FRIEND_TEST_ALL_PREFIXES(CertVerifyProcTest, DigiNotarCerts);
   FRIEND_TEST_ALL_PREFIXES(CertVerifyProcTest, TestHasTooLongValidity);
 
   // Performs the actual verification using the desired underlying
-  // cryptographic library.
+  // cryptographic library. On entry, |verify_result->verified_cert|
+  // is set to |cert|, the unverified chain. If no chain is built, the
+  // value must be left untouched.
   virtual int VerifyInternal(X509Certificate* cert,
                              const std::string& hostname,
                              int flags,
                              CRLSet* crl_set,
                              const CertificateList& additional_trust_anchors,
                              CertVerifyResult* verify_result) = 0;
 
   // Returns true if |cert| is explicitly blacklisted.
   static bool IsBlacklisted(X509Certificate* cert);
 
@@ skipping 21 matching lines @@
   // requirement they expire within 7 years after the effective date of the BRs
   // (i.e. by 1 July 2019).
   static bool HasTooLongValidity(const X509Certificate& cert);
 
   DISALLOW_COPY_AND_ASSIGN(CertVerifyProc);
 };
 
 }  // namespace net
 
 #endif  // NET_CERT_CERT_VERIFY_PROC_H_