base: Update the include paths of base/string_piece.h to its new location.

base/strings/sys_string_conversions_posix.cc

 // 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.
 
 #include "base/strings/sys_string_conversions.h"
 
 #include <wchar.h>
 
-#include "base/string_piece.h"
+#include "base/strings/string_piece.h"
 #include "base/utf_string_conversions.h"
 
 namespace base {
 
 std::string SysWideToUTF8(const std::wstring& wide) {
   // In theory this should be using the system-provided conversion rather
   // than our ICU, but this will do for now.
   return WideToUTF8(wide);
 }
 std::wstring SysUTF8ToWide(const StringPiece& utf8) {
@@ skipping 132 matching lines @@
         break;
     }
   }
 
   return out;
 }
 
 #endif  // OS_CHROMEOS
 
 }  // namespace base