Added test for util.printx() and make it match spec.

fpdfsdk/javascript/PublicMethods.cpp

Index: fpdfsdk/javascript/PublicMethods.cpp
diff --git a/fpdfsdk/javascript/PublicMethods.cpp b/fpdfsdk/javascript/PublicMethods.cpp
index b85111bed7db65c5d0430a362dc0894e8a5ab243..6f9f514bd08826f460ae55766a947f79b8a176aa 100644
--- a/fpdfsdk/javascript/PublicMethods.cpp
+++ b/fpdfsdk/javascript/PublicMethods.cpp
@@ -1440,23 +1440,18 @@ FX_BOOL CJS_PublicMethods::AFSpecial_Format(
     case 1:
       cFormat = "99999-9999";
       break;
-    case 2: {
-      std::string NumberStr;
-      util::printx("9999999999", strSrc, NumberStr);
-      if (NumberStr.length() >= 10)
+    case 2:
+      if (util::printx("9999999999", strSrc).length() >= 10)
         cFormat = "(999) 999-9999";
       else
         cFormat = "999-9999";
       break;
-    }
     case 3:
       cFormat = "999-99-9999";
       break;
   }
 
-  std::string strDes;
-  util::printx(cFormat, strSrc, strDes);
-  Value = CFX_WideString::FromLocal(strDes.c_str());
+  Value = CFX_WideString::FromLocal(util::printx(cFormat, strSrc).c_str());
   return TRUE;
 }
 
@@ -1578,22 +1573,15 @@ FX_BOOL CJS_PublicMethods::AFSpecial_Keystroke(
       cFormat = "99999";
       break;
     case 1:
-      // cFormat = "99999-9999";
       cFormat = "999999999";
       break;
-    case 2: {
-      std::string NumberStr;
-      util::printx("9999999999", strSrc, NumberStr);
+    case 2:
       if (strSrc.length() + wstrChange.length() > 7)
-        // cFormat = "(999) 999-9999";
         cFormat = "9999999999";
       else
-        // cFormat = "999-9999";
         cFormat = "9999999";
       break;
-    }
     case 3:
-      // cFormat = "999-99-9999";
       cFormat = "999999999";
       break;
   }