Review and cleanup lint warnings.

fpdfsdk/src/pdfwindow/PWL_Signature.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/include/pdfwindow/PWL_Signature.h"
+
+#include <string>
+
 #include "fpdfsdk/include/pdfwindow/PWL_Icon.h"
 #include "fpdfsdk/include/pdfwindow/PWL_Label.h"
-#include "fpdfsdk/include/pdfwindow/PWL_Signature.h"
 #include "fpdfsdk/include/pdfwindow/PWL_Utils.h"
 #include "fpdfsdk/include/pdfwindow/PWL_Wnd.h"
 
 CPWL_Signature_Image::CPWL_Signature_Image() : m_pImage(NULL) {}
 
 CPWL_Signature_Image::~CPWL_Signature_Image() {}
 
 void CPWL_Signature_Image::SetImage(CFX_DIBSource* pImage) {
   m_pImage = pImage;
 }
@@ skipping 147 matching lines @@
         pDevice, pUser2Device, PWL_ICONTYPE_FOXIT,
         CPWL_Utils::GetCenterSquare(GetClientRect()),
         CPWL_Color(COLORTYPE_RGB, 0.91f, 0.855f, 0.92f),
         CPWL_Color(COLORTYPE_TRANSPARENT), 255);
   }
 }
 
 void CPWL_Signature::GetThisAppearanceStream(CFX_ByteTextBuf& sAppStream) {
   CPWL_Wnd::GetThisAppearanceStream(sAppStream);
 }