Add size metric into Heap Stats.

include/v8-profiler.h

Index: include/v8-profiler.h
diff --git a/include/v8-profiler.h b/include/v8-profiler.h
index 77419493990ffc813baf4235153cc23a691481aa..3b019cff7158940dcfe0cbdb5e0c7ff937fbe400 100644
--- a/include/v8-profiler.h
+++ b/include/v8-profiler.h
@@ -429,8 +429,9 @@ class V8EXPORT HeapProfiler {
    * time interval entry contains information on the current heap objects
    * population size. The method also updates aggregated statistics and
    * reports updates for all previous time intervals via the OutputStream
-   * object. Updates on each time interval are provided as pairs of time
-   * interval index and updated heap objects count.
+   * object. Updates on each time interval are provided as a triplet. It has
+   * time interval index, updated heap objects count and updated heap objects
+   * size.
    *
    * StartHeapObjectsTracking must be called before the first call to this
    * method.