Fixup incorrect include guards.

core/include/fxcodec/fx_codec_flate.h

 // Copyright 2015 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 CORE_INCLUDE_FXCODEC_FX_CODEC_FLATE_H_
+#define CORE_INCLUDE_FXCODEC_FX_CODEC_FLATE_H_
+
 #include "third_party/zlib_v128/zlib.h"
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
 // Note: Some of these return Z_* status codes from zlib.h.
 void* FPDFAPI_FlateInit(void* (*alloc_func)(void*, unsigned int, unsigned int),
                         void (*free_func)(void*, void*));
 void FPDFAPI_FlateInput(void* context,
                         const unsigned char* src_buf,
                         unsigned int src_size);
 int FPDFAPI_FlateOutput(void* context,
                         unsigned char* dest_buf,
                         unsigned int dest_size);
 int FPDFAPI_FlateGetAvailIn(void* context);
 int FPDFAPI_FlateGetAvailOut(void* context);
 void FPDFAPI_FlateEnd(void* context);
 
 #ifdef __cplusplus
 }  // extern "C"
 #endif
+
+#endif  // CORE_INCLUDE_FXCODEC_FX_CODEC_FLATE_H_