Move FPDFAPI_FlateInit() prototype and friends to .h file

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
+
+#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