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

runtime/vm/heap.cc

Index: runtime/vm/heap.cc
diff --git a/runtime/vm/heap.cc b/runtime/vm/heap.cc
index 670c86844caed7e4c7c0b5183a84b2d33539387b..2b319fd931feb51ecee1d9ec7494e0460fff78a4 100644
--- a/runtime/vm/heap.cc
+++ b/runtime/vm/heap.cc
@@ -647,8 +647,20 @@ int64_t Heap::PeerCount() const {
 
 
 int64_t Heap::HashCount() const {
-  return
-      new_weak_tables_[kHashes]->count() + old_weak_tables_[kHashes]->count();
+  return new_weak_tables_[kHashes]->count() +
+      old_weak_tables_[kHashes]->count();
+}
+
+
+int64_t Heap::ObjectIdCount() const {
+  return new_weak_tables_[kObjectIds]->count() +
+      old_weak_tables_[kObjectIds]->count();
+}
+
+
+void Heap::ResetObjectIdTable() {
+  new_weak_tables_[kObjectIds]->Reset();
+  old_weak_tables_[kObjectIds]->Reset();
 }