Fix IWYU in fxcrt headers.

core/include/fxcrt/fx_stream.h

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #ifndef _FX_STREAM_H_
 #define _FX_STREAM_H_
-#ifndef _FX_MEMORY_H_
+
 #include "fx_memory.h"
-#endif
+#include "fx_string.h"
+
 void* FX_OpenFolder(FX_LPCSTR path);
 void* FX_OpenFolder(FX_LPCWSTR path);
 FX_BOOL FX_GetNextFile(void* handle, CFX_ByteString& filename, FX_BOOL& bFolder);
 FX_BOOL FX_GetNextFile(void* handle, CFX_WideString& filename, FX_BOOL& bFolder);
 void FX_CloseFolder(void* handle);
 FX_WCHAR FX_GetFolderSeparator();
 FX_DEFINEHANDLE(FX_HFILE)
 #if _FXM_PLATFORM_ == _FXM_PLATFORM_WINDOWS_
 #define FX_FILESIZE                     FX_INT32
 #else
@@ skipping 169 matching lines @@
 
     virtual FX_BOOL                     ReadNextBlock(FX_BOOL bRestart = FALSE) = 0;
 
     virtual FX_LPCBYTE          GetBlockBuffer() = 0;
 
     virtual size_t                      GetBlockSize() = 0;
 
     virtual FX_FILESIZE         GetBlockOffset() = 0;
 };
 #endif