fix a crash issue in _CMapLookupCallback BUG=382242 R=palmer@chromium.org Review URL: https://codereview.chromium.org/341333004

diff --git a/core/include/fpdfapi/fpdf_objects.h b/core/include/fpdfapi/fpdf_objects.h
index a41ff08..1b7cb94 100644
--- a/core/include/fpdfapi/fpdf_objects.h
+++ b/core/include/fpdfapi/fpdf_objects.h

@@ -49,6 +49,11 @@
         return m_ObjNum;
     }
 
+    FX_DWORD                            GetGenNum() const
+    {
+        return m_GenNum;
+    }
+
     FX_BOOL					IsIdentical(CPDF_Object* pObj) const;
 
     CPDF_Object*			Clone(FX_BOOL bDirect = FALSE) const;
@@ -90,9 +95,11 @@
     CPDF_Object()
     {
         m_ObjNum = 0;
+        m_GenNum = 0;
     }
 
     FX_DWORD 				m_ObjNum;
+    FX_DWORD				m_GenNum;
 
     void					Destroy();
 

diff --git a/core/src/fpdfapi/fpdf_parser/fpdf_parser_objects.cpp b/core/src/fpdfapi/fpdf_parser/fpdf_parser_objects.cpp
index 6c93bcb..e945ab5 100644
--- a/core/src/fpdfapi/fpdf_parser/fpdf_parser_objects.cpp
+++ b/core/src/fpdfapi/fpdf_parser/fpdf_parser_objects.cpp

@@ -1271,9 +1271,15 @@
     if (objnum == 0 || pObj == NULL) {
         return;
     }
-    FX_LPVOID value;
+    FX_LPVOID value = NULL;
     if (m_IndirectObjs.Lookup((FX_LPVOID)(FX_UINTPTR)objnum, value)) {
-        ((CPDF_Object*)value)->Destroy();
+        if (value)
+        {
+            if (pObj->GetGenNum() <= ((CPDF_Object*)value)->GetGenNum())
+                return;
+            else 
+                ((CPDF_Object*)value)->Destroy();
+         }         
     }
     pObj->m_ObjNum = objnum;
     m_IndirectObjs.SetAt((FX_LPVOID)(FX_UINTPTR)objnum, pObj);

diff --git a/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp b/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
index b9e5359..3bfd37f 100644
--- a/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
+++ b/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp

@@ -1384,6 +1384,7 @@
     m_Syntax.RestorePos(SavedPos);
     if (pObj && !objnum) {
         pObj->m_ObjNum = real_objnum;
+        pObj->m_GenNum = gennum;
     }
     return pObj;
 }