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

core/fpdfapi/fpdf_page/cpdf_pattern.h

Index: core/fpdfapi/fpdf_page/cpdf_pattern.h
diff --git a/core/fpdfapi/fpdf_page/cpdf_pattern.h b/core/fpdfapi/fpdf_page/cpdf_pattern.h
index d6ef49c7fb66e97d31ffe3f830da51057c7ab4e9..983c9eab3f6485468a65a201abc81ecc133bbcd2 100644
--- a/core/fpdfapi/fpdf_page/cpdf_pattern.h
+++ b/core/fpdfapi/fpdf_page/cpdf_pattern.h
@@ -27,19 +27,19 @@ class CPDF_Pattern {
   CPDF_Document* document() { return m_pDocument; }
   CPDF_Object* pattern_obj() { return m_pPatternObj; }
   CFX_Matrix* pattern_to_form() { return &m_Pattern2Form; }
-  CFX_Matrix* parent_matrix() { return &m_ParentMatrix; }
+  const CFX_Matrix& parent_matrix() const { return m_ParentMatrix; }
 
  protected:
   CPDF_Pattern(PatternType type,
                CPDF_Document* pDoc,
                CPDF_Object* pObj,
-               const CFX_Matrix* pParentMatrix);
+               const CFX_Matrix& parentMatrix);
 
   const PatternType m_PatternType;
   CPDF_Document* const m_pDocument;
   CPDF_Object* const m_pPatternObj;
   CFX_Matrix m_Pattern2Form;
-  CFX_Matrix m_ParentMatrix;
+  const CFX_Matrix m_ParentMatrix;
 };
 
 #endif  // CORE_FPDFAPI_FPDF_PAGE_CPDF_PATTERN_H_