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

core/fpdfapi/fpdf_page/fpdf_page_doc.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 "core/fdrm/crypto/include/fx_crypt.h"
 #include "core/fpdfapi/fpdf_font/cpdf_type1font.h"
@@ skipping 298 matching lines @@
     csData->RemoveRef();
     if (csData->use_count() == 0) {
       csData->get()->ReleaseCS();
       csData->reset(nullptr);
     }
   }
 }
 
 CPDF_Pattern* CPDF_DocPageData::GetPattern(CPDF_Object* pPatternObj,
                                            FX_BOOL bShading,
-                                           const CFX_Matrix* matrix) {
+                                           const CFX_Matrix& matrix) {
   if (!pPatternObj)
     return nullptr;
 
   CPDF_CountedPattern* ptData = nullptr;
   auto it = m_PatternMap.find(pPatternObj);
   if (it != m_PatternMap.end()) {
     ptData = it->second;
     if (ptData->get()) {
       return ptData->AddRef();
     }
@@ skipping 180 matching lines @@
 }
 
 CPDF_CountedPattern* CPDF_DocPageData::FindPatternPtr(
     CPDF_Object* pPatternObj) const {
   if (!pPatternObj)
     return nullptr;
 
   auto it = m_PatternMap.find(pPatternObj);
   return it != m_PatternMap.end() ? it->second : nullptr;
 }