[runtime] Fix effect of setting .prototype on generator functions.

src/objects.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <sstream>
 
@@ skipping 11807 matching lines @@
   if (!value->IsJSReceiver()) {
     // Copy the map so this does not affect unrelated functions.
     // Remove map transitions because they point to maps with a
     // different prototype.
     Handle<Map> new_map = Map::Copy(handle(function->map()), "SetPrototype");
 
     JSObject::MigrateToMap(function, new_map);
     new_map->SetConstructor(*value);
     new_map->set_non_instance_prototype(true);
     Isolate* isolate = new_map->GetIsolate();
+
     construct_prototype = handle(
-        function->context()->native_context()->initial_object_prototype(),
+        IsGeneratorFunction(function->shared()->kind())
+            ? function->context()
+                  ->native_context()
+                  ->initial_generator_prototype()
+            : function->context()->native_context()->initial_object_prototype(),
         isolate);
   } else {
     function->map()->set_non_instance_prototype(false);
   }
 
   return SetInstancePrototype(function, construct_prototype);
 }
 
 
 bool JSFunction::RemovePrototype() {
@@ skipping 6459 matching lines @@
   if (cell->value() != *new_value) {
     cell->set_value(*new_value);
     Isolate* isolate = cell->GetIsolate();
     cell->dependent_code()->DeoptimizeDependentCodeGroup(
         isolate, DependentCode::kPropertyCellChangedGroup);
   }
 }
 
 }  // namespace internal
 }  // namespace v8