Cleanup string passing in core/fpdf*

Return strings where possible.
Add missing consts to strings passed by ref.
Convert non-const cases to pointers.
Rename a few methods to be clearer.

Change-Id: I86569bc1744f539e6dd67fc73649b272c016328c
Reviewed-on: https://pdfium-review.googlesource.com/3951
Commit-Queue: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Nicolás Peña <npm@chromium.org>
diff --git a/fpdfsdk/javascript/Field.cpp b/fpdfsdk/javascript/Field.cpp
index 12c3508..c7dc260 100644
--- a/fpdfsdk/javascript/Field.cpp
+++ b/fpdfsdk/javascript/Field.cpp
@@ -2482,12 +2482,10 @@
   if (!pFormControl)
     return false;
 
-  CPDF_DefaultAppearance FieldAppearance = pFormControl->GetDefaultAppearance();
-
-  CFX_ByteString csFontNameTag;
   float fFontSize;
-  FieldAppearance.GetFont(csFontNameTag, fFontSize);
-  vp << (int)fFontSize;
+  CPDF_DefaultAppearance FieldAppearance = pFormControl->GetDefaultAppearance();
+  FieldAppearance.GetFont(&fFontSize);
+  vp << static_cast<int>(fFontSize);
   return true;
 }