Disable invalid DCHECK_EQ in serializer.cc

BUG=none
R=mvstanton@chromium.org,yangguo@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/791363002

Cr-Commit-Position: refs/heads/master@{#25769}

src/serialize.cc

@@ -491,7 +491,9 @@ RootIndexMap::RootIndexMap(Isolate* isolate) {
       if (LookupEntry(map_, heap_object, false) != NULL) {
         // Some root values are initialized to the empty FixedArray();
         // Do not add them to the map.
-        DCHECK_EQ(isolate->heap()->empty_fixed_array(), heap_object);
+        // TODO(yangguo): This assert is not true. Some roots like
+        // instanceof_cache_answer can be e.g. null.
+        // DCHECK_EQ(isolate->heap()->empty_fixed_array(), heap_object);
       } else {
         SetValue(LookupEntry(map_, heap_object, true), i);
       }