CPDF_Document::LoadPattern() and friends always have a valid matrix.

core/fpdfapi/fpdf_page/fpdf_page_parser_old.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/fpdfapi/fpdf_page/pageint.h"
 
 #include <limits.h>
 
@@ skipping 646 matching lines @@
       m_StreamArray.resize(m_nStreams);
     else
       m_Status = Done;
   } else {
     m_Status = Done;
   }
 }
 
 void CPDF_ContentParser::Start(CPDF_Form* pForm,
                                CPDF_AllStates* pGraphicStates,
-                               CFX_Matrix* pParentMatrix,
+                               const CFX_Matrix* pParentMatrix,
                                CPDF_Type3Char* pType3Char,
                                int level) {
   m_pType3Char = pType3Char;
   m_pObjectHolder = pForm;
   m_bForm = TRUE;
   CFX_Matrix form_matrix = pForm->m_pFormDict->GetMatrixBy("Matrix");
   if (pGraphicStates) {
     form_matrix.Concat(pGraphicStates->m_CTM);
   }
   CPDF_Array* pBBox = pForm->m_pFormDict->GetArrayBy("BBox");
@@ skipping 135 matching lines @@
       }
       m_Status = Done;
       return;
     }
     steps++;
     if (pPause && pPause->NeedToPauseNow()) {
       break;
     }
   }
 }