Move fxcrt::{Byte,Wide}Strings with std::move().

Remove some string copies in barcode that were noticed whilst
looking for moves.

Change-Id: Ieda34d00f633576ba1f0dca283dcdabfb36f236c
Reviewed-on: https://pdfium-review.googlesource.com/35410
Reviewed-by: dsinclair <dsinclair@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>
diff --git a/fpdfsdk/cpdfsdk_interform.cpp b/fpdfsdk/cpdfsdk_interform.cpp
index 1e24746..379a8b9 100644
--- a/fpdfsdk/cpdfsdk_interform.cpp
+++ b/fpdfsdk/cpdfsdk_interform.cpp
@@ -10,6 +10,7 @@
 #include <memory>
 #include <sstream>
 #include <string>
+#include <utility>
 #include <vector>
 
 #include "core/fpdfapi/page/cpdf_page.h"
@@ -322,13 +323,11 @@
       WideString script = action.GetJavaScript();
       if (!script.IsEmpty()) {
         WideString Value = sValue;
-
         IJS_Runtime::ScopedEventContext pContext(pRuntime);
         pContext->OnField_Format(pFormField, Value, true);
-
         Optional<IJS_Runtime::JS_Error> err = pContext->RunScript(script);
         if (!err) {
-          sValue = Value;
+          sValue = std::move(Value);
           bFormatted = true;
         }
       }