Fix a bunch of sign mismatch warnings.

core/src/fxcodec/codec/fx_codec_jpeg.cpp

 // 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
 
 #include <setjmp.h>
 
 #include "../../../include/fxcodec/fx_codec.h"
 #include "../../../include/fxcrt/fx_safe_types.h"
@@ skipping 175 matching lines @@
   }
   jpeg_start_compress(&cinfo, TRUE);
   _JpegEmbedIccProfile(&cinfo, icc_buf, icc_length);
   JSAMPROW row_pointer[1];
   JDIMENSION row;
   while (cinfo.next_scanline < cinfo.image_height) {
     const uint8_t* src_scan = pSource->GetScanline(cinfo.next_scanline);
     if (nComponents > 1) {
       uint8_t* dest_scan = line_buf;
       if (nComponents == 3) {
-        for (int i = 0; i < width; i++) {
+        for (FX_DWORD i = 0; i < width; i++) {
           dest_scan[0] = src_scan[2];
           dest_scan[1] = src_scan[1];
           dest_scan[2] = src_scan[0];
           dest_scan += 3;
           src_scan += Bpp;
         }
       } else {
-        for (int i = 0; i < pitch; i++) {
+        for (FX_DWORD i = 0; i < pitch; i++) {
           *dest_scan++ = ~*src_scan++;
         }
       }
       row_pointer[0] = line_buf;
     } else {
       row_pointer[0] = (uint8_t*)src_scan;
     }
     row = cinfo.next_scanline;
     jpeg_write_scanlines(&cinfo, row_pointer, 1);
     if (cinfo.next_scanline == row) {
@@ skipping 492 matching lines @@
   }
   if (avail_buf_ptr != NULL) {
     *avail_buf_ptr = NULL;
     if (((FXJPEG_Context*)pContext)->m_SrcMgr.bytes_in_buffer > 0) {
       *avail_buf_ptr =
           (uint8_t*)((FXJPEG_Context*)pContext)->m_SrcMgr.next_input_byte;
     }
   }
   return (FX_DWORD)((FXJPEG_Context*)pContext)->m_SrcMgr.bytes_in_buffer;
 }