Fix issue 822: handling of JSObject::elements in CalculateNetworkSize.

src/profile-generator.cc

Index: src/profile-generator.cc
diff --git a/src/profile-generator.cc b/src/profile-generator.cc
index 1d1aa812bc09e32ab00fe37f4086250ca1dc055d..cd46badf0997772958336fcfdd024f36752944b0 100644
--- a/src/profile-generator.cc
+++ b/src/profile-generator.cc
@@ -1379,10 +1379,10 @@ int HeapSnapshot::CalculateNetworkSize(JSObject* obj) {
   int size = obj->Size();
   // If 'properties' and 'elements' are non-empty (thus, non-shared),
   // take their size into account.
-  if (FixedArray::cast(obj->properties())->length() != 0) {
+  if (obj->properties() != Heap::empty_fixed_array()) {
     size += obj->properties()->Size();
   }
-  if (FixedArray::cast(obj->elements())->length() != 0) {
+  if (obj->elements() != Heap::empty_fixed_array()) {
     size += obj->elements()->Size();
   }
   // For functions, also account non-empty context and literals sizes.