Subtract instead of adding the negation.

fpdfsdk/fxedit/fxet_edit.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/fxedit/include/fxet_edit.h"
 
 #include <algorithm>
 
@@ skipping 201 matching lines @@
                   rcResult = pOldRect->m_rcLine;
                   rcResult.Union(pNewRect->m_rcLine);
                 } else {
                   fWidthDiff =
                       pNewRect->m_rcLine.Width() - pOldRect->m_rcLine.Width();
                   rcResult = pNewRect->m_rcLine;
                   if (fWidthDiff > 0.0f) {
                     rcResult.left = rcResult.right - fWidthDiff;
                   } else {
                     rcResult.left = rcResult.right;
-                    rcResult.right += (-fWidthDiff);
+                    rcResult.right -= fWidthDiff;
                   }
                 }
                 m_RefreshRects.Add(rcResult);
               }
             } else {
               rcResult = pOldRect->m_rcLine;
               rcResult.Union(pNewRect->m_rcLine);
               m_RefreshRects.Add(rcResult);
             }
           }
@@ skipping 2795 matching lines @@
     if (m_bOprNotify && m_pOprNotify)
       m_pOprNotify->OnAddUndo(pEditUndoItem);
   }
 }
 
 void CFX_Edit::AddUndoItem(IFX_Edit_UndoItem* pUndoItem) {
   m_Undo.AddItem(pUndoItem);
   if (m_bOprNotify && m_pOprNotify)
     m_pOprNotify->OnAddUndo(pUndoItem);
 }