Add check for trivial string equality

core/fxcrt/fx_basic_bstring.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 <stddef.h>
 
 #include <algorithm>
 #include <cctype>
@@ skipping 184 matching lines @@
 
 bool CFX_ByteString::operator==(const CFX_ByteStringC& str) const {
   if (!m_pData)
     return str.IsEmpty();
 
   return m_pData->m_nDataLength == str.GetLength() &&
          FXSYS_memcmp(m_pData->m_String, str.c_str(), str.GetLength()) == 0;
 }
 
 bool CFX_ByteString::operator==(const CFX_ByteString& other) const {
+  if (m_pData == other.m_pData)
+    return true;
+
   if (IsEmpty())
     return other.IsEmpty();
 
   if (other.IsEmpty())
     return false;
 
   return other.m_pData->m_nDataLength == m_pData->m_nDataLength &&
          FXSYS_memcmp(other.m_pData->m_String, m_pData->m_String,
                       m_pData->m_nDataLength) == 0;
 }
@@ skipping 773 matching lines @@
     fraction %= scale;
     scale /= 10;
   }
   return buf_size;
 }
 CFX_ByteString CFX_ByteString::FormatFloat(FX_FLOAT d, int precision) {
   FX_CHAR buf[32];
   FX_STRSIZE len = FX_ftoa(d, buf);
   return CFX_ByteString(buf, len);
 }