Remove FX_STRSIZE and replace with size_t

BUG=pdfium:828

Change-Id: I5c40237433ebabaeabdb43aec9cdf783e41dfe16
Reviewed-on: https://pdfium-review.googlesource.com/13230
Reviewed-by: dsinclair <dsinclair@chromium.org>
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
diff --git a/fpdfsdk/javascript/util.cpp b/fpdfsdk/javascript/util.cpp
index 3fe7a86..c4b1568 100644
--- a/fpdfsdk/javascript/util.cpp
+++ b/fpdfsdk/javascript/util.cpp
@@ -297,8 +297,8 @@
 WideString util::printx(const WideString& wsFormat,
                         const WideString& wsSource) {
   WideString wsResult;
-  FX_STRSIZE iSourceIdx = 0;
-  FX_STRSIZE iFormatIdx = 0;
+  size_t iSourceIdx = 0;
+  size_t iFormatIdx = 0;
   CaseMode eCaseMode = kPreserveCase;
   bool bEscaped = false;
   while (iFormatIdx < wsFormat.GetLength()) {