Fixes Object::SetAccessor to return false if the prop is unconfigurable.

test/unittests/api/v8-object-unittest.cc

Index: test/unittests/api/v8-object-unittest.cc
diff --git a/test/unittests/api/v8-object-unittest.cc b/test/unittests/api/v8-object-unittest.cc
new file mode 100644
index 0000000000000000000000000000000000000000..5d6ca804ad0303e994194e83d2cd90ef18a2b4bc
--- /dev/null
+++ b/test/unittests/api/v8-object-unittest.cc
@@ -0,0 +1,39 @@
+// Copyright 2017 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 "include/v8.h"
+#include "test/unittests/test-utils.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace v8 {
+namespace {
+
+using ObjectTest = TestWithContext;
+
+void accessor_name_getter_callback(Local<Name>,
+                                   const PropertyCallbackInfo<Value>&) {}
+
+TEST_F(ObjectTest, SetAccessorWhenUnconfigurablePropAlreadyDefined) {
+  Context::Scope context_scope(context());
+
+  TryCatch try_catch(isolate());
+
+  Local<Object> global = context()->Global();
+  Local<String> property_name =
+      String::NewFromUtf8(isolate(), "foo", NewStringType::kNormal)
+          .ToLocalChecked();
+
+  PropertyDescriptor prop_desc;
+  prop_desc.set_configurable(false);
+  global->DefineProperty(context(), property_name, prop_desc).ToChecked();
+
+  Maybe<bool> result = global->SetAccessor(context(), property_name,
+                                           accessor_name_getter_callback);
+  ASSERT_TRUE(result.IsJust());
+  ASSERT_FALSE(result.FromJust());
+  ASSERT_FALSE(try_catch.HasCaught());
+}
+
+}  // namespace
+}  // namespace v8