Add a function for parsing RFC 5280's "TBSCertificate".

net/cert/internal/test_helpers.cc

 // Copyright 2015 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.
 
 #include "net/cert/internal/test_helpers.h"
 
 #include "base/base64.h"
 #include "base/base_paths.h"
 #include "base/files/file_util.h"
 #include "base/path_service.h"
@@ skipping 65 matching lines @@
         mapping.value->assign(pem_tokenizer.data());
 
         // Mark the mapping as having been satisfied.
         mapping.value = nullptr;
       }
     }
   }
 
   // Ensure that all specified blocks were found.
   for (const auto& mapping : mappings_copy) {
-    if (mapping.value) {
+    if (mapping.value && !mapping.optional) {
       return ::testing::AssertionFailure() << "PEM block missing: "
                                            << mapping.block_name;
     }
   }
 
   return ::testing::AssertionSuccess();
 }
 
 }  // namespace net