Fix RefPtr's move assignment operator

Source/wtf/RefPtrTest.cpp

+// Copyright 2014 The Chromium 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 "config.h"
+#include "wtf/RefPtr.h"
+
+#include "wtf/text/StringImpl.h"
+#include <gtest/gtest.h>
+
+namespace {
+
+TEST(RefPtrTest, Basic)
+{
+    RefPtr<StringImpl> string;
+    EXPECT_TRUE(!string);
+    string = StringImpl::create("test");
+    EXPECT_TRUE(!!string);
+    string.clear();
+    EXPECT_TRUE(!string);
+}
+
+#if COMPILER_SUPPORTS(CXX_RVALUE_REFERENCES)
+TEST(RefPtrTest, MoveAssignmentOperator)
+{
+    RefPtr<StringImpl> a = StringImpl::create("a");
+    RefPtr<StringImpl> b = StringImpl::create("b");
+    // FIXME: Instead of explicitly casting to RefPtr<StringImpl>&& here, we should use std::move, but that
+    // requires us to have a standard library that supports move semantics.
+    b = static_cast<RefPtr<StringImpl>&&>(a);
+    EXPECT_TRUE(!!b);
+    EXPECT_TRUE(!a);
+}
+#endif
+
+}