Replace a #define in cfwl_scrollbar.cpp

-- convert a pre-existing const to constexpr

Change-Id: Ib9f3a295a132ee8225ce7aeca347a3a00c9b9cf4
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/83555
Auto-Submit: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>

xfa/fwl/cfwl_scrollbar.cpp

diff --git a/xfa/fwl/cfwl_scrollbar.cpp b/xfa/fwl/cfwl_scrollbar.cpp
index b967911..f622d766 100644
--- a/xfa/fwl/cfwl_scrollbar.cpp
+++ b/xfa/fwl/cfwl_scrollbar.cpp
@@ -19,11 +19,11 @@
 #include "xfa/fwl/cfwl_themepart.h"
 #include "xfa/fwl/ifwl_themeprovider.h"
 
-#define FWL_SCROLLBAR_Elapse 500
 
 namespace {
 
-const float kMinThumbSize = 5.0f;
+constexpr int kScrollbarElapsedMsecs = 500;
+constexpr float kMinThumbSize = 5.0f;
 
 }  // namespace
 
@@ -339,7 +339,7 @@
 
   if (!SendEvent()) {
     m_pTimer = std::make_unique<CFX_Timer>(GetFWLApp()->GetTimerHandler(), this,
-                                           FWL_SCROLLBAR_Elapse);
+                                           kScrollbarElapsedMsecs);
   }
 }