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

test/cctest/test-heap-profiler.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 //
 // Tests for heap profiler
 
 #include "v8.h"
 
 #include "cctest.h"
 #include "heap-profiler.h"
 #include "snapshot.h"
 #include "utils-inl.h"
@@ skipping 396 matching lines @@
 
 TEST(HeapEntryIdsAndGC) {
   v8::HandleScope scope;
   LocalContext env;
 
   CompileRun(
       "function A() {}\n"
       "function B(x) { this.x = x; }\n"
       "var a = new A();\n"
       "var b = new B(a);");
+  v8::Local<v8::String> s1_str = v8_str("s1");
+  v8::Local<v8::String> s2_str = v8_str("s2");
   const v8::HeapSnapshot* snapshot1 =
-      v8::HeapProfiler::TakeSnapshot(v8_str("s1"));
+      v8::HeapProfiler::TakeSnapshot(s1_str);
 
   HEAP->CollectAllGarbage(i::Heap::kNoGCFlags);
 
   const v8::HeapSnapshot* snapshot2 =
-      v8::HeapProfiler::TakeSnapshot(v8_str("s2"));
+      v8::HeapProfiler::TakeSnapshot(s2_str);
+
+  // Second snapshot has one more string, it is it's name 's2'.
+  CHECK_EQ_SNAPSHOT_OBJECT_ID(
+    snapshot1->GetMaxSnapshotJSObjectId(),
+    snapshot2->GetMaxSnapshotJSObjectId());
 
   const v8::HeapGraphNode* global1 = GetGlobalObject(snapshot1);
   const v8::HeapGraphNode* global2 = GetGlobalObject(snapshot2);
   CHECK_NE_SNAPSHOT_OBJECT_ID(0, global1->GetId());
   CHECK_EQ_SNAPSHOT_OBJECT_ID(global1->GetId(), global2->GetId());
   const v8::HeapGraphNode* A1 =
       GetProperty(global1, v8::HeapGraphEdge::kProperty, "A");
   CHECK_NE(NULL, A1);
   const v8::HeapGraphNode* A2 =
       GetProperty(global2, v8::HeapGraphEdge::kProperty, "A");
@@ skipping 925 matching lines @@
   // Dipose the persistent handles in a different order.
   p_AAA.Dispose();
   CHECK_EQ(global_handle_count + 2,
            v8::HeapProfiler::GetPersistentHandleCount());
   p_CCC.Dispose();
   CHECK_EQ(global_handle_count + 1,
            v8::HeapProfiler::GetPersistentHandleCount());
   p_BBB.Dispose();
   CHECK_EQ(global_handle_count, v8::HeapProfiler::GetPersistentHandleCount());
 }