[heap] Filter out non-heap values when tracing wrappers

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 6f030b306997d2b7f90f366f8ca1a936a8eb30e8..168febcf989e486b3efca855308912f0a6918a87 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -5671,11 +5671,10 @@ void Heap::TracePossibleWrapper(JSObject* js_object) {
 }
 
 void Heap::RegisterExternallyReferencedObject(Object** object) {
+  // The embedder is not aware of whether numbers are materialized as heap
+  // objects are just passed around as Smis.
+  if (!(*object)->IsHeapObject()) return;

[Hannes Payer (out of office), 2017/04/27 14:46:18]

Do you still want to keep the nullptr check? Or can it never be null?

[Michael Lippautz, 2017/04/27 14:47:50]

If it is a heap object it cannot be null, as this would be represented as an
empty handle on the embedder side.

If we get a tagged null pointer we will crash in the DCHECK, which is what we
want to see.

   HeapObject* heap_object = HeapObject::cast(*object);
-  if (heap_object == nullptr) {
-    // We might encounter non-empty handles that point to nullptr.
-    return;
-  }
   DCHECK(Contains(heap_object));
   if (FLAG_incremental_marking_wrappers && incremental_marking()->IsMarking()) {
     IncrementalMarking::MarkGrey(this, heap_object);