Expose last seen heap object id via v8 public api.

src/heap-profiler.cc

Index: src/heap-profiler.cc
diff --git a/src/heap-profiler.cc b/src/heap-profiler.cc
index 2e971a51b4076ac3c4ad29327c509ab13d13653b..975d6f4221c9162a79ae37413bb2362839f78108 100644
--- a/src/heap-profiler.cc
+++ b/src/heap-profiler.cc
@@ -97,7 +97,7 @@ void HeapProfiler::StopHeapObjectsTracking() {
 }
 
 
-void HeapProfiler::PushHeapObjectsStats(v8::OutputStream* stream) {
+SnapshotObjectId HeapProfiler::PushHeapObjectsStats(v8::OutputStream* stream) {
   ASSERT(Isolate::Current()->heap_profiler() != NULL);
   return Isolate::Current()->heap_profiler()->PushHeapObjectsStatsImpl(stream);
 }
@@ -158,8 +158,8 @@ void HeapProfiler::StartHeapObjectsTrackingImpl() {
 }
 
 
-void HeapProfiler::PushHeapObjectsStatsImpl(OutputStream* stream) {
-  snapshots_->PushHeapObjectsStats(stream);
+SnapshotObjectId HeapProfiler::PushHeapObjectsStatsImpl(OutputStream* stream) {
+  return snapshots_->PushHeapObjectsStats(stream);
 }