Fix negative font rendering on Mac by reversing matrix c component.

core/fxge/apple/fx_apple_platform.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 "core/fxcrt/fx_system.h"
 
 #if _FXM_PLATFORM_ == _FXM_PLATFORM_APPLE_
 
@@ skipping 54 matching lines @@
   for (int i = 0; i < nChars; i++) {
     glyph_indices[i] = pCharPos[i].m_ExtGID;
     if (bNegSize)
       glyph_positions[i].x = -pCharPos[i].m_OriginX;
     else
       glyph_positions[i].x = pCharPos[i].m_OriginX;
     glyph_positions[i].y = pCharPos[i].m_OriginY;
   }
   if (bNegSize) {
     new_matrix.a = -new_matrix.a;
+    new_matrix.c = -new_matrix.c;
   } else {
     new_matrix.b = -new_matrix.b;
     new_matrix.d = -new_matrix.d;
   }
   quartz2d.setGraphicsTextMatrix(pContext, &new_matrix);
   return quartz2d.drawGraphicsString(pContext, pFont->GetPlatformFont(),
                                      font_size, glyph_indices, glyph_positions,
                                      nChars, argb, nullptr);
 }
 
@@ skipping 94 matching lines @@
   if (m_pPlatformFont) {
     CQuartz2D& quartz2d =
         static_cast<CApplePlatform*>(CFX_GEModule::Get()->GetPlatformData())
             ->m_quartz2d;
     quartz2d.DestroyFont(m_pPlatformFont);
     m_pPlatformFont = nullptr;
   }
 }
 
 #endif  // _FXM_PLATFORM_  == _FXM_PLATFORM_APPLE_