Introduce CertErrors::ToDebugString().

net/cert/internal/cert_errors.cc

Index: net/cert/internal/cert_errors.cc
diff --git a/net/cert/internal/cert_errors.cc b/net/cert/internal/cert_errors.cc
index 00500304302332c3d7a03f3e0543d563d13f02b1..d00d7fb0e3bf200b6c47ec1c71783262621a7ee3 100644
--- a/net/cert/internal/cert_errors.cc
+++ b/net/cert/internal/cert_errors.cc
@@ -54,6 +54,16 @@ void CertErrors::AddWith2DerParams(CertErrorType type,
   AddWithParam(type, base::MakeUnique<CertErrorParamsDer2>(der1, der2));
 }
 
+std::string CertErrors::ToDebugString() const {
+  std::string str;
+  for (const auto& error : errors_) {
+    if (!str.empty())
+      str += "\n";
+    str += error.type;
+  }
+  return str;
+}
+
 ScopedCertErrorsCertContext::ScopedCertErrorsCertContext(
     CertErrors* parent,
     const ParsedCertificate* cert,