Add checks to runtime functions.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 74af575afbfc8f0d3b32f65e040e7670d67753e4..158de1452bd2b50e4e081950a0f1d276091cffc8 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -7533,16 +7533,13 @@ MaybeObject* JSFunction::SetPrototype(Object* value) {
 }
 
 
-Object* JSFunction::RemovePrototype() {
+void JSFunction::RemovePrototype() {
   Context* native_context = context()->native_context();
   Map* no_prototype_map = shared()->is_classic_mode()
       ? native_context->function_without_prototype_map()
       : native_context->strict_mode_function_without_prototype_map();
 
-  if (map() == no_prototype_map) {
-    // Be idempotent.
-    return this;
-  }
+  if (map() == no_prototype_map) return;
 
   ASSERT(map() == (shared()->is_classic_mode()
                    ? native_context->function_map()
@@ -7550,13 +7547,11 @@ Object* JSFunction::RemovePrototype() {
 
   set_map(no_prototype_map);
   set_prototype_or_initial_map(no_prototype_map->GetHeap()->the_hole_value());
-  return this;
 }
 
 
-Object* JSFunction::SetInstanceClassName(String* name) {
+void JSFunction::SetInstanceClassName(String* name) {
   shared()->set_instance_class_name(name);
-  return this;
 }