Add CFX_ByteStringC::CharAt() to avoid c_str() and casts

core/fxcrt/fx_xml_composer.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 "core/fxcrt/xml_int.h"
 
 #include "core/fxcrt/include/fx_xml.h"
 
 void FX_XML_SplitQualifiedName(const CFX_ByteStringC& bsFullName,
                                CFX_ByteStringC& bsSpace,
                                CFX_ByteStringC& bsName) {
-  if (bsFullName.IsEmpty()) {
+  if (bsFullName.IsEmpty())
     return;
-  }
-  int32_t iStart = 0;
-  for (; iStart < bsFullName.GetLength(); iStart++) {
-    if (bsFullName.GetAt(iStart) == ':') {
-      break;
-    }
-  }
-  if (iStart >= bsFullName.GetLength()) {
+
+  FX_STRSIZE iStart = bsFullName.Find(':');
+  if (iStart == -1) {
     bsName = bsFullName;
   } else {
-    bsSpace = CFX_ByteStringC(bsFullName.c_str(), iStart);
-    iStart++;
-    bsName = CFX_ByteStringC(bsFullName.c_str() + iStart,
-                             bsFullName.GetLength() - iStart);
+    bsSpace = bsFullName.Mid(0, iStart);
+    bsName = bsFullName.Mid(iStart + 1);
   }
 }
+
 void CXML_Element::SetTag(const CFX_ByteStringC& qSpace,
                           const CFX_ByteStringC& tagname) {
   m_QSpaceName = qSpace;
   m_TagName = tagname;
 }
 void CXML_Element::SetTag(const CFX_ByteStringC& qTagName) {
   ASSERT(!qTagName.IsEmpty());
   CFX_ByteStringC bsSpace, bsName;
   FX_XML_SplitQualifiedName(qTagName, bsSpace, bsName);
   m_QSpaceName = bsSpace;
   m_TagName = bsName;
 }