Add more instrumentation for Code::CopyFrom crasher.

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index 67759e67b63aee8552c827f92e2c68add42d02f2..e32391381b9282545bcf087549628e183388a28e 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -3805,6 +3805,8 @@ MaybeObject* Heap::CreateCode(const CodeDesc& desc,
   }
   // Allow self references to created code object by patching the handle to
   // point to the newly allocated Code object.
+  CHECK(code->IsCode());
+  CHECK(code->relocation_info()->IsByteArray());
   if (!self_reference.is_null()) {
     *(self_reference.location()) = code;
   }
@@ -3813,6 +3815,8 @@ MaybeObject* Heap::CreateCode(const CodeDesc& desc,
   // that are dereferenced during the copy to point directly to the actual heap
   // objects. These pointers can include references to the code object itself,
   // through the self_reference parameter.
+  CHECK(code->IsCode());
+  CHECK(code->relocation_info()->IsByteArray());
   code->CopyFrom(desc);
 
 #ifdef VERIFY_HEAP