Reduce signed/unsigned comparison warnings

core/fpdfapi/fpdf_parser/cpdf_array.cpp

 // Copyright 2016 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/fpdfapi/fpdf_parser/include/cpdf_array.h"
 
 #include "core/fpdfapi/fpdf_parser/include/cpdf_name.h"
 #include "core/fpdfapi/fpdf_parser/include/cpdf_number.h"
@@ skipping 29 matching lines @@
 CPDF_Array* CPDF_Array::AsArray() {
   return this;
 }
 
 const CPDF_Array* CPDF_Array::AsArray() const {
   return this;
 }
 
 CPDF_Object* CPDF_Array::Clone(FX_BOOL bDirect) const {
   CPDF_Array* pCopy = new CPDF_Array();
-  for (int i = 0; i < GetCount(); i++) {
+  for (size_t i = 0; i < GetCount(); i++) {
     CPDF_Object* value = m_Objects.GetAt(i);
     pCopy->m_Objects.Add(value->Clone(bDirect));
   }
   return pCopy;
 }
 
 CFX_FloatRect CPDF_Array::GetRect() {
   CFX_FloatRect rect;
   if (!IsArray() || m_Objects.GetSize() != 4)
     return rect;
@@ skipping 137 matching lines @@
   ASSERT(IsArray());
   CPDF_Number* pNumber = new CPDF_Number(f);
   Add(pNumber);
 }
 
 void CPDF_Array::AddReference(CPDF_IndirectObjectHolder* pDoc,
                               uint32_t objnum) {
   ASSERT(IsArray());
   Add(new CPDF_Reference(pDoc, objnum));
 }