Convert int* references to FX_STRSIZE

Through out the code base there are numerous places where variables
are declared using a signed integer type when interacting with the
string classes, since they assume that FX_STRSIZE is 'int'. As part of
changing the underling type of FX_STRSIZE to be unsigned, these
locations are being changed to use FX_STRSIZE. This is necessary as
part of converting the type, but has been broken off into a separate CL,
since it should be low risk.

Some related cleanups that are low risk are included as part of
this CL.

BUG=pdfium:828

Change-Id: Ifaae54ad195ccde0fe8672f71271d29a6ebd65fd
Reviewed-on: https://pdfium-review.googlesource.com/12210
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Henrique Nakashima <hnakashima@chromium.org>
Reviewed-by: dsinclair <dsinclair@chromium.org>
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
diff --git a/fpdfsdk/javascript/Document.cpp b/fpdfsdk/javascript/Document.cpp
index 9b82147..d8934a4 100644
--- a/fpdfsdk/javascript/Document.cpp
+++ b/fpdfsdk/javascript/Document.cpp
@@ -1016,7 +1016,7 @@
     return false;
   }
   CFX_WideString wsFilePath = m_pFormFillEnv->JS_docGetFilePath();
-  int32_t i = wsFilePath.GetLength() - 1;
+  FX_STRSIZE i = wsFilePath.GetLength() - 1;
   for (; i >= 0; i--) {
     if (wsFilePath[i] == L'\\' || wsFilePath[i] == L'/')
       break;
diff --git a/fpdfsdk/javascript/PublicMethods.cpp b/fpdfsdk/javascript/PublicMethods.cpp
index ff1d4fb..ee5bbba 100644
--- a/fpdfsdk/javascript/PublicMethods.cpp
+++ b/fpdfsdk/javascript/PublicMethods.cpp
@@ -366,7 +366,7 @@
   bool bExit = false;
   bool bBadFormat = false;
 
-  int i = 0;
+  FX_STRSIZE i = 0;
   int j = 0;
 
   while (i < format.GetLength()) {
@@ -394,7 +394,7 @@
       case 't': {
         int oldj = j;
         int nSkip = 0;
-        int remaining = format.GetLength() - i - 1;
+        FX_STRSIZE remaining = format.GetLength() - i - 1;
 
         if (remaining == 0 || format[i + 1] != c) {
           switch (c) {
@@ -628,10 +628,10 @@
   int nMin = JS_GetMinFromTime(dDate);
   int nSec = JS_GetSecFromTime(dDate);
 
-  int i = 0;
+  FX_STRSIZE i = 0;
   while (i < format.GetLength()) {
     wchar_t c = format[i];
-    int remaining = format.GetLength() - i - 1;
+    FX_STRSIZE remaining = format.GetLength() - i - 1;
     sPart = L"";
     switch (c) {
       case 'y':