Don't attempt to forward declare StringPiece.

net/base/x509_cert_types.h

 // Copyright (c) 2011 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_BASE_X509_CERT_TYPES_H_
 #define NET_BASE_X509_CERT_TYPES_H_
 #pragma once
 
 #include <string.h>
 
 #include <set>
 #include <string>
 #include <vector>
 
+#include "base/string_piece.h"
 #include "build/build_config.h"
 #include "net/base/net_export.h"
 
 #if defined(OS_MACOSX)
 #include <Security/x509defs.h>
 #endif
 
 namespace base {
 class Time;
-class StringPiece;
 }  // namespace base
 
 namespace net {
 
 class X509Certificate;
 
 // SHA-1 fingerprint (160 bits) of a certificate.
 struct SHA1Fingerprint {
   bool Equals(const SHA1Fingerprint& other) const {
     return memcmp(data, other.data, sizeof(data)) == 0;
@@ skipping 111 matching lines @@
 // Attempts to parse |raw_date|, an ASN.1 date/time string encoded as
 // |format|, and writes the result into |*time|. If an invalid date is
 // specified, or if parsing fails, returns false, and |*time| will not be
 // updated.
 bool ParseCertificateDate(const base::StringPiece& raw_date,
                           CertDateFormat format,
                           base::Time* time);
 }  // namespace net
 
 #endif  // NET_BASE_X509_CERT_TYPES_H_