[bootstrapper] clear extras utils object after usage.

The extras utils object will no longer be needed after
bootstrapping, and can be cleared.

R=jochen@chromium.org

Review-Url: https://codereview.chromium.org/2670093002
Cr-Commit-Position: refs/heads/master@{#42908}

src/bootstrapper.cc

@@ -3132,6 +3132,7 @@ void Genesis::ConfigureUtilsObject(GlobalContextType context_type) {
 
   // The utils object can be removed for cases that reach this point.
   native_context()->set_natives_utils_object(heap()->undefined_value());
+  native_context()->set_extras_utils_object(heap()->undefined_value());
 }
 
 

src/contexts.h

@@ -222,7 +222,7 @@ enum ContextLookupFlags {
     error_message_for_code_gen_from_strings)                                   \
   V(ERRORS_THROWN_INDEX, Smi, errors_thrown)                                   \
   V(EXTRAS_EXPORTS_OBJECT_INDEX, JSObject, extras_binding_object)              \
-  V(EXTRAS_UTILS_OBJECT_INDEX, JSObject, extras_utils_object)                  \
+  V(EXTRAS_UTILS_OBJECT_INDEX, Object, extras_utils_object)                    \
   V(FAST_ALIASED_ARGUMENTS_MAP_INDEX, Map, fast_aliased_arguments_map)         \
   V(FAST_TEMPLATE_INSTANTIATIONS_CACHE_INDEX, FixedArray,                      \
     fast_template_instantiations_cache)                                        \