Reduce signed/unsigned comparison warnings

fpdfsdk/javascript/JS_Value.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 "fpdfsdk/javascript/JS_Value.h"
 
 #include <time.h>
 
@@ skipping 875 matching lines @@
 
   if (originals.size() != 1 || originals[0].GetType() != CJS_Value::VT_object ||
       originals[0].IsArrayObject()) {
     return result;
   }
   v8::Local<v8::Object> pObj = originals[0].ToV8Object();
   result[0] = CJS_Value(pRuntime);  // Make unknown.
 
   va_list ap;
   va_start(ap, nKeywords);
-  for (int i = 0; i < nKeywords; ++i) {
+  for (size_t i = 0; i < nKeywords; ++i) {
     const wchar_t* property = va_arg(ap, const wchar_t*);
     v8::Local<v8::Value> v8Value =
         FXJS_GetObjectElement(pRuntime->GetIsolate(), pObj, property);
     if (!v8Value->IsUndefined())
       result[i] = CJS_Value(pRuntime, v8Value, CJS_Value::VT_unknown);
   }
   va_end(ap);
   return result;
 }