Don't overwrite transitions in SetPropertyIgnoreAttributes.

test/cctest/test-api.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1981 matching lines @@
   LocalContext env;
   env->Global()->Set(v8_str("Child"), child->GetFunction());
   CompileRun("var child = new Child;"
              "child.age = 10;");
   ExpectBoolean("child.hasOwnProperty('age')", false);
   ExpectInt32("child.age", 10);
   ExpectInt32("child.accessor_age", 10);
 }
 
 
+THREADED_TEST(EmptyInterceptorBreakTransitions) {
+  v8::HandleScope scope(CcTest::isolate());
+  Handle<FunctionTemplate> templ = FunctionTemplate::New(CcTest::isolate());
+  AddInterceptor(templ, EmptyInterceptorGetter, EmptyInterceptorSetter);
+  LocalContext env;
+  env->Global()->Set(v8_str("Constructor"), templ->GetFunction());
+  CompileRun("var o1 = new Constructor;"
+             "o1.a = 1;"  // Ensure a and x share the descriptor array.
+             "Object.defineProperty(o1, 'x', {value: 10});");
+  CompileRun("var o2 = new Constructor;"
+             "o2.a = 1;"
+             "Object.defineProperty(o2, 'x', {value: 10});");
+}
+
+
 THREADED_TEST(EmptyInterceptorDoesNotShadowJSAccessors) {
   v8::Isolate* isolate = CcTest::isolate();
   v8::HandleScope scope(isolate);
   Handle<FunctionTemplate> parent = FunctionTemplate::New(isolate);
   Handle<FunctionTemplate> child = FunctionTemplate::New(isolate);
   child->Inherit(parent);
   AddInterceptor(child, EmptyInterceptorGetter, EmptyInterceptorSetter);
   LocalContext env;
   env->Global()->Set(v8_str("Child"), child->GetFunction());
   CompileRun("var child = new Child;"
@@ skipping 19805 matching lines @@
   context->Global()->Set(v8_str("P"), templ->NewInstance());
   CompileRun(
       "function C1() {"
       "  this.x = 23;"
       "};"
       "C1.prototype = P;"
       "for (var i = 0; i < 4; i++ ) {"
       "  new C1();"
       "}");
 }