Fix some sign comparison warnings.

fpdfsdk/src/javascript/Document.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 "../../include/javascript/JavaScript.h"
 #include "../../include/javascript/IJavaScript.h"
 #include "../../include/javascript/JS_Define.h"
 #include "../../include/javascript/JS_Object.h"
@@ skipping 1190 matching lines @@
   return cbRet;
 }
 
 CFX_WideString Document::CutString(CFX_WideString cbFrom) {
   size_t iLength = cbFrom.GetLength();
   pdfium::base::CheckedNumeric<size_t> iSize = sizeof(wchar_t);
   iSize *= (iLength + 1);
   wchar_t* pResult = (wchar_t*)malloc(iSize.ValueOrDie());
   wchar_t* pFrom = (wchar_t*)cbFrom.GetBuffer(iLength);
 
-  for (int i = 0; i < iLength; i++) {
+  for (size_t i = 0; i < iLength; i++) {
     if (pFrom[i] == L'\\' || pFrom[i] == L'/') {
       pResult[i] = L'\0';
       break;
     }
     pResult[i] = pFrom[i];
   }
   pResult[iLength] = L'\0';
 
   cbFrom.ReleaseBuffer();
   CFX_WideString cbRet = CFX_WideString(pResult);
@@ skipping 704 matching lines @@
   CFX_DWordArray DelArray;
 
   for (int j = DelArray.GetSize() - 1; j >= 0; j--) {
     m_DelayData.RemoveAt(DelArray[j]);
   }
 }
 
 CJS_Document* Document::GetCJSDoc() const {
   return static_cast<CJS_Document*>(m_pJSObject);
 }