I'd like to add HeapSnapshot::GetMaxSnapshotJSObjectId function.

src/profile-generator.h

Index: src/profile-generator.h
diff --git a/src/profile-generator.h b/src/profile-generator.h
index d9a1319b87bc9f9f5480b2106afa8242e54e981f..8010538cc9096d9f928533e3d69668e79cac21df 100644
--- a/src/profile-generator.h
+++ b/src/profile-generator.h
@@ -35,8 +35,6 @@
 namespace v8 {
 namespace internal {
 
-typedef uint32_t SnapshotObjectId;
-
 class TokenEnumerator {
  public:
   TokenEnumerator();
@@ -647,6 +645,9 @@ class HeapSnapshot {
   HeapEntry* gc_subroot(int index) { return gc_subroot_entries_[index]; }
   List<HeapEntry*>* entries() { return &entries_; }
   size_t raw_entries_size() { return raw_entries_size_; }
+  SnapshotObjectId max_snapshot_js_object_id() const {
+    return max_snapshot_js_object_id_;
+  }
 
   void AllocateEntries(
       int entries_count, int children_count, int retainers_count);
@@ -687,6 +688,7 @@ class HeapSnapshot {
   List<HeapEntry*> entries_;
   bool entries_sorted_;
   size_t raw_entries_size_;
+  SnapshotObjectId max_snapshot_js_object_id_;
 
   friend class HeapSnapshotTester;