Add a hash map for a raw object to id mapping, this table will be used during snapshot writing in o…

runtime/vm/heap.h

Index: runtime/vm/heap.h
diff --git a/runtime/vm/heap.h b/runtime/vm/heap.h
index 4639c2602b5803deacf23486e9740704088fef84..22a109ecfece5909be36e3ea415148d391a1ae6d 100644
--- a/runtime/vm/heap.h
+++ b/runtime/vm/heap.h
@@ -42,6 +42,7 @@ class Heap {
   enum WeakSelector {
     kPeers = 0,
     kHashes,
+    kObjectIds,
     kNumWeakSelectors
   };
 
@@ -189,6 +190,17 @@ class Heap {
   }
   int64_t HashCount() const;
 
+  // Associate an id with an object (used when serializing an object).
+  // A non-existant id is equal to 0.
+  void SetObjectId(RawObject* raw_obj, intptr_t object_id) {
+    SetWeakEntry(raw_obj, kObjectIds, object_id);
+  }
+  intptr_t GetObjectId(RawObject* raw_obj) const {
+    return GetWeakEntry(raw_obj, kObjectIds);
+  }
+  int64_t ObjectIdCount() const;
+  void ResetObjectIdTable();
+
   // Used by the GC algorithms to propagate weak entries.
   intptr_t GetWeakEntry(RawObject* raw_obj, WeakSelector sel) const;
   void SetWeakEntry(RawObject* raw_obj, WeakSelector sel, intptr_t val);