Make down-conversion explicit from CFX_ByteString to CFX_ByteStringC.

fpdfsdk/pdfwindow/PWL_ScrollBar.cpp

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #include "fpdfsdk/pdfwindow/PWL_ScrollBar.h"
 
 #include "core/include/fxge/fx_ge.h"
 #include "fpdfsdk/pdfwindow/PWL_Utils.h"
@@ skipping 652 matching lines @@
 }
 
 void CPWL_ScrollBar::GetThisAppearanceStream(CFX_ByteTextBuf& sAppStream) {
   CFX_FloatRect rectWnd = GetWindowRect();
 
   if (IsVisible() && !rectWnd.IsEmpty()) {
     CFX_ByteTextBuf sButton;
 
     sButton << "q\n";
     sButton << "0 w\n"
-            << CPWL_Utils::GetColorAppStream(GetBackgroundColor(), TRUE);
+            << CPWL_Utils::GetColorAppStream(GetBackgroundColor(), TRUE)
+                   .AsByteStringC();
     sButton << rectWnd.left << " " << rectWnd.bottom << " "
             << rectWnd.right - rectWnd.left << " "
             << rectWnd.top - rectWnd.bottom << " re b Q\n";
 
     sAppStream << sButton;
   }
 }
 
 void CPWL_ScrollBar::DrawThisAppearance(CFX_RenderDevice* pDevice,
                                         CFX_Matrix* pUser2Device) {
@@ skipping 506 matching lines @@
   if (m_bMinOrMax)
     m_sData.SubSmall();
   else
     m_sData.AddSmall();
 
   if (FXSYS_memcmp(&m_sData, &sTemp, sizeof(PWL_SCROLL_PRIVATEDATA)) != 0) {
     MovePosButton(TRUE);
     NotifyScrollWindow();
   }
 }