Add support of rebuilding crossrefs with compressed objects.

Change-Id: I0743c34f0206f85828570430edb9f62b6b0cdbb5
Reviewed-on: https://pdfium-review.googlesource.com/37315
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Art Snake <art-snake@yandex-team.ru>

core/fpdfapi/parser/cpdf_object_stream.h

diff --git a/core/fpdfapi/parser/cpdf_object_stream.h b/core/fpdfapi/parser/cpdf_object_stream.h
index 816c1be..44aa8f7 100644
--- a/core/fpdfapi/parser/cpdf_object_stream.h
+++ b/core/fpdfapi/parser/cpdf_object_stream.h
@@ -33,6 +33,9 @@
   bool HasObject(uint32_t obj_number) const;
   std::unique_ptr<CPDF_Object> ParseObject(CPDF_IndirectObjectHolder* pObjList,
                                            uint32_t obj_number) const;
+  const std::map<uint32_t, uint32_t>& objects_offsets() const {
+    return objects_offsets_;
+  }
 
  protected:
   explicit CPDF_ObjectStream(const CPDF_Stream* stream);

core/fpdfapi/parser/cpdf_parser.cpp

diff --git a/core/fpdfapi/parser/cpdf_parser.cpp b/core/fpdfapi/parser/cpdf_parser.cpp
index d4ad065..4d38357 100644
--- a/core/fpdfapi/parser/cpdf_parser.cpp
+++ b/core/fpdfapi/parser/cpdf_parser.cpp
@@ -650,8 +650,6 @@
       const FX_FILESIZE obj_pos = numbers[0].second;
       const uint32_t obj_num = numbers[0].first;
       const uint32_t gen_num = numbers[1].first;
-      if (obj_num < kMaxObjectNumber)
-        cross_ref_table->AddNormal(obj_num, gen_num, obj_pos);
 
       m_pSyntax->SetPos(obj_pos);
       const std::unique_ptr<CPDF_Stream> pStream =
@@ -664,6 +662,17 @@
             pdfium::MakeUnique<CPDF_CrossRefTable>(
                 ToDictionary(pStream->GetDict()->Clone())));
       }
+
+      if (obj_num < kMaxObjectNumber) {
+        cross_ref_table->AddNormal(obj_num, gen_num, obj_pos);
+        if (const auto object_stream =
+                CPDF_ObjectStream::Create(pStream.get())) {
+          for (const auto& it : object_stream->objects_offsets()) {
+            if (it.first < kMaxObjectNumber)
+              cross_ref_table->AddCompressed(it.first, obj_num);
+          }
+        }
+      }
     }
     numbers.clear();
   }