Make CPDF_Object::GetString() a virtual method.

core/src/fpdfdoc/doc_viewerPreferences.cpp

Index: core/src/fpdfdoc/doc_viewerPreferences.cpp
diff --git a/core/src/fpdfdoc/doc_viewerPreferences.cpp b/core/src/fpdfdoc/doc_viewerPreferences.cpp
index eb824eb5a48a1412bab64ef8bd0e945e36c4feaa..12d56dd9b2a8985564685bdec87d5b1ab8a989cf 100644
--- a/core/src/fpdfdoc/doc_viewerPreferences.cpp
+++ b/core/src/fpdfdoc/doc_viewerPreferences.cpp
@@ -15,19 +15,17 @@ FX_BOOL CPDF_ViewerPreferences::IsDirectionR2L() const
 {
     CPDF_Dictionary *pDict = m_pDoc->GetRoot();
     pDict = pDict->GetDict(FX_BSTRC("ViewerPreferences"));
-    if (!pDict)	{
+    if (!pDict)
         return FALSE;
-    }
-    return FX_BSTRC("R2L") == pDict->GetString(FX_BSTRC("Direction"));
+    return pDict->GetStringAt("Direction") == "R2L";
 }
 FX_BOOL CPDF_ViewerPreferences::PrintScaling() const
 {
     CPDF_Dictionary *pDict = m_pDoc->GetRoot();
     pDict = pDict->GetDict(FX_BSTRC("ViewerPreferences"));
-    if (!pDict)	{
+    if (!pDict)
         return TRUE;
-    }
-    return FX_BSTRC("None") != pDict->GetString(FX_BSTRC("PrintScaling"));
+    return pDict->GetStringAt("PrintScaling") != "None";
 }
 int32_t CPDF_ViewerPreferences::NumCopies() const
 {
@@ -56,5 +54,5 @@ CFX_ByteString CPDF_ViewerPreferences::Duplex() const
     if (!pDict) {
         return FX_BSTRC("None");
     }
-    return pDict->GetString(FX_BSTRC("Duplex"));
+    return pDict->GetStringAt("Duplex");
 }