Instrument code entry slot recording to help with crash investigation.

src/heap/mark-compact.cc

Index: src/heap/mark-compact.cc
diff --git a/src/heap/mark-compact.cc b/src/heap/mark-compact.cc
index ad0c58e4a8d53e61c5c459caec33d9299184d065..08fce434c34bb3c7f5fa9466e4316961bb38a393 100644
--- a/src/heap/mark-compact.cc
+++ b/src/heap/mark-compact.cc
@@ -3933,6 +3933,8 @@ void MarkCompactCollector::RecordCodeEntrySlot(HeapObject* host, Address slot,
   Page* source_page = Page::FromAddress(reinterpret_cast<Address>(host));
   if (target_page->IsEvacuationCandidate() &&
       !ShouldSkipEvacuationSlotRecording(host)) {
+    // TODO(ulan): remove this check after investigating crbug.com/414964.
+    CHECK(target->IsCode());
     RememberedSet<OLD_TO_OLD>::InsertTyped(source_page, CODE_ENTRY_SLOT, slot);
   }
 }