Make CPDF_Object::GetString() a virtual method.

core/src/fpdfapi/fpdf_page/fpdf_page_graph_state.cpp

Index: core/src/fpdfapi/fpdf_page/fpdf_page_graph_state.cpp
diff --git a/core/src/fpdfapi/fpdf_page/fpdf_page_graph_state.cpp b/core/src/fpdfapi/fpdf_page/fpdf_page_graph_state.cpp
index 70d0743f58b5678fe87f632f712644d5b52ae4ed..5f55021a7197a5307d08e693170ada8d3d2d2741 100644
--- a/core/src/fpdfapi/fpdf_page/fpdf_page_graph_state.cpp
+++ b/core/src/fpdfapi/fpdf_page/fpdf_page_graph_state.cpp
@@ -521,7 +521,8 @@ void CPDF_AllStates::ProcessExtGS(CPDF_Dictionary* pGS, CPDF_StreamContentParser
                     }
                     CPDF_Array* pFont = (CPDF_Array*)pObject;
                     m_TextState.GetModify()->m_FontSize = pFont->GetNumber(1);
-                    m_TextState.SetFont(pParser->FindFont(pFont->GetString(0)));
+                    m_TextState.SetFont(
+                        pParser->FindFont(pFont->GetStringAt(0)));
                     break;
                 }
             case FXBSTR_ID('T', 'R', 0, 0):
@@ -538,7 +539,7 @@ void CPDF_AllStates::ProcessExtGS(CPDF_Dictionary* pGS, CPDF_StreamContentParser
             case FXBSTR_ID('B', 'M', 0, 0):	{
                     CFX_ByteString mode;
                     if (pObject->GetType() == PDFOBJ_ARRAY) {
-                        mode = ((CPDF_Array*)pObject)->GetString(0);
+                        mode = ((CPDF_Array*)pObject)->GetStringAt(0);
                     } else {
                         mode = pObject->GetString();
                     }