Implement heap profiler memory usage reporting.

src/heap-profiler.cc

Index: src/heap-profiler.cc
diff --git a/src/heap-profiler.cc b/src/heap-profiler.cc
index 975d6f4221c9162a79ae37413bb2362839f78108..bb0b0ee57c034e0b8756433144e45dd89db31907 100644
--- a/src/heap-profiler.cc
+++ b/src/heap-profiler.cc
@@ -168,6 +168,14 @@ void HeapProfiler::StopHeapObjectsTrackingImpl() {
 }
 
 
+size_t HeapProfiler::GetUsedMemorySize() {
+  HeapProfiler* profiler = Isolate::Current()->heap_profiler();
+  ASSERT(profiler != NULL);
+  size_t size = profiler->snapshots_->GetUsedMemorySize();
+  return size;
+}
+
+
 int HeapProfiler::GetSnapshotsCount() {
   HeapProfiler* profiler = Isolate::Current()->heap_profiler();
   ASSERT(profiler != NULL);