Oilpan: when snapshotting type-specific pages use GCInfo of the page.

Source/platform/heap/Heap.cpp

Index: Source/platform/heap/Heap.cpp
diff --git a/Source/platform/heap/Heap.cpp b/Source/platform/heap/Heap.cpp
index 111562a5ce26c4e116118796c3a6c9f0b8a67811..9b964b1b07693dbd31d148cdad0d1be7362d9f37 100644
--- a/Source/platform/heap/Heap.cpp
+++ b/Source/platform/heap/Heap.cpp
@@ -1400,7 +1400,8 @@ void HeapPage<Header>::snapshot(TracedValue* json, ThreadState::SnapshotInfo* in
             continue;
         }
 
-        size_t tag = info->getClassTag(header->gcInfo());
+        const GCInfo* gcinfo = header->gcInfo() ? header->gcInfo() : gcInfo();
+        size_t tag = info->getClassTag(gcinfo);
         size_t age = header->age();
         if (json)
             json->pushInteger(tag);