Allow self_size to be larger than 2GB in heap snapshots.

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index dfde26565b1393bfa4de6f36b7844e3698c29586..2c7db3be1656f10d475dd8e1de71a89ed374cdd6 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -6971,6 +6971,13 @@ SnapshotObjectId HeapGraphNode::GetId() const {
 
 
 int HeapGraphNode::GetSelfSize() const {
+  size_t size = ToInternal(this)->self_size();
+  CHECK(size <= static_cast<size_t>(internal::kMaxInt));
+  return static_cast<int>(size);
+}
+
+
+size_t HeapGraphNode::GetShallowSize() const {
   return ToInternal(this)->self_size();
 }