Use std::unordered_map for CFDE_CSSStyleSheet::m_StringCache

xfa/fde/css/fde_cssstylesheet.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 "xfa/fde/css/fde_cssstylesheet.h"
 
 #include <memory>
 
@@ skipping 84 matching lines @@
       case FDE_CSSRULETYPE_FontFace:
         ((CFDE_CSSFontFaceRule*)pRule)->~CFDE_CSSFontFaceRule();
         break;
       default:
         ASSERT(FALSE);
         break;
     }
   }
   m_RuleArray.RemoveAll();
   m_Selectors.RemoveAll();
-  m_StringCache.RemoveAll();
+  m_StringCache.clear();
   delete m_pAllocator;
   m_pAllocator = nullptr;
 }
 uint32_t CFDE_CSSStyleSheet::AddRef() {
   return ++m_wRefCount;
 }
 uint32_t CFDE_CSSStyleSheet::Release() {
   uint32_t dwRefCount = --m_wRefCount;
   if (dwRefCount == 0) {
     delete this;
@@ skipping 52 matching lines @@
         eStatus = LoadImportRule(pSyntax);
         break;
       case FDE_CSSSYNTAXSTATUS_PageRule:
         eStatus = LoadPageRule(pSyntax);
         break;
       default:
         break;
     }
   } while (eStatus >= FDE_CSSSYNTAXSTATUS_None);
   m_Selectors.RemoveAll();
-  m_StringCache.RemoveAll();
+  m_StringCache.clear();
   return eStatus != FDE_CSSSYNTAXSTATUS_Error;
 }
 FDE_CSSSYNTAXSTATUS CFDE_CSSStyleSheet::LoadMediaRule(
     CFDE_CSSSyntaxParser* pSyntax) {
   uint32_t dwMediaList = 0;
   CFDE_CSSMediaRule* pMediaRule = NULL;
   for (;;) {
     switch (pSyntax->DoSyntaxParse()) {
       case FDE_CSSSYNTAXSTATUS_MediaType: {
         int32_t iLen;
@@ skipping 307 matching lines @@
       return NULL;
     }
   }
   if (pPersudoFirst == NULL) {
     return pFirst;
   } else {
     pPersudoLast->SetNext(pFirst);
     return pPersudoFirst;
   }
 }