Don't attempt to forward declare StringPiece.

net/base/big_endian.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_BIG_ENDIAN_H_
 #define NET_BASE_BIG_ENDIAN_H_
 #pragma once
 
 #include "base/basictypes.h"
+#include "base/string_piece.h"
 #include "net/base/net_export.h"
 
-namespace base {
-class StringPiece;
-}
-
 namespace net {
 
 // Read an integer (signed or unsigned) from |buf| in Big Endian order.
 // Note: this loop is unrolled with -O1 and above.
 // NOTE(szym): glibc dns-canon.c and SpdyFrameBuilder use
 // ntohs(*(uint16_t*)ptr) which is potentially unaligned.
 // This would cause SIGBUS on ARMv5 or earlier and ARMv6-M.
 template<typename T>
 inline void ReadBigEndian(const char buf[], T* out) {
   *out = buf[0];
@@ skipping 72 matching lines @@
   bool Write(T v);
 
   char* ptr_;
   char* end_;
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_BIG_ENDIAN_H_