Expose last seen heap object id via v8 public api.

test/cctest/test-heap-profiler.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 //
 // Tests for heap profiler
 
 #include <ctype.h>
 
 #include "v8.h"
 
 #include "cctest.h"
 #include "hashmap.h"
@@ skipping 673 matching lines @@
   int eos_signaled_;
   int updates_written_;
   uint32_t entries_count_;
   uint32_t entries_size_;
   int intervals_count_;
   int first_interval_index_;
 };
 
 }  // namespace
 
-static TestStatsStream GetHeapStatsUpdate() {
+static TestStatsStream GetHeapStatsUpdate(
+    v8::SnapshotObjectId* object_id = NULL) {
   TestStatsStream stream;
-  v8::HeapProfiler::PushHeapObjectsStats(&stream);
+  v8::SnapshotObjectId last_seen_id =
+      v8::HeapProfiler::PushHeapObjectsStats(&stream);
+  if (object_id)
+    *object_id = last_seen_id;
   CHECK_EQ(1, stream.eos_signaled());
   return stream;
 }
 
 
 TEST(HeapSnapshotObjectsStats) {
   v8::HandleScope scope;
   LocalContext env;
 
   v8::HeapProfiler::StartHeapObjectsTracking();
   // We have to call GC 5 times. In other case the garbage will be
   // the reason of flakiness.
   for (int i = 0; i < 5; ++i) {
     HEAP->CollectAllGarbage(i::Heap::kNoGCFlags);
   }
 
+  v8::SnapshotObjectId initial_id;
   {
     // Single chunk of data expected in update. Initial data.
-    TestStatsStream stats_update = GetHeapStatsUpdate();
+    TestStatsStream stats_update = GetHeapStatsUpdate(&initial_id);
     CHECK_EQ(1, stats_update.intervals_count());
     CHECK_EQ(1, stats_update.updates_written());
     CHECK_LT(0, stats_update.entries_size());
     CHECK_EQ(0, stats_update.first_interval_index());
   }
 
   // No data expected in update because nothing has happened.
-  CHECK_EQ(0, GetHeapStatsUpdate().updates_written());
+  v8::SnapshotObjectId same_id;
+  CHECK_EQ(0, GetHeapStatsUpdate(&same_id).updates_written());
+  CHECK_EQ_SNAPSHOT_OBJECT_ID(initial_id, same_id);
+
   {
+    v8::SnapshotObjectId additional_string_id;
     v8::HandleScope inner_scope_1;
     v8_str("string1");
     {
       // Single chunk of data with one new entry expected in update.
-      TestStatsStream stats_update = GetHeapStatsUpdate();
+      TestStatsStream stats_update = GetHeapStatsUpdate(&additional_string_id);
+      CHECK_LT(same_id, additional_string_id);
       CHECK_EQ(1, stats_update.intervals_count());
       CHECK_EQ(1, stats_update.updates_written());
       CHECK_LT(0, stats_update.entries_size());
       CHECK_EQ(1, stats_update.entries_count());
       CHECK_EQ(2, stats_update.first_interval_index());
     }
 
     // No data expected in update because nothing happened.
-    CHECK_EQ(0, GetHeapStatsUpdate().updates_written());
+    v8::SnapshotObjectId last_id;
+    CHECK_EQ(0, GetHeapStatsUpdate(&last_id).updates_written());
+    CHECK_EQ_SNAPSHOT_OBJECT_ID(additional_string_id, last_id);
 
     {
       v8::HandleScope inner_scope_2;
       v8_str("string2");
 
       uint32_t entries_size;
       {
         v8::HandleScope inner_scope_3;
         v8_str("string3");
         v8_str("string4");
@@ skipping 852 matching lines @@
   const v8::HeapGraphNode* global_object =
       GetProperty(global, v8::HeapGraphEdge::kProperty, "global_object");
   CHECK_NE(NULL, global_object);
   const v8::HeapGraphNode* properties =
       GetProperty(global_object, v8::HeapGraphEdge::kInternal, "properties");
   CHECK_EQ(NULL, properties);
   const v8::HeapGraphNode* elements =
       GetProperty(global_object, v8::HeapGraphEdge::kInternal, "elements");
   CHECK_EQ(NULL, elements);
 }