Factor out NullExecutionContext from unittest files.

Source/core/testing/NullExecutionContext.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 "core/testing/NullExecutionContext.h"
+
+namespace WebCore {
+
+namespace {
+
+class NullEventQueue FINAL : public EventQueue {
+public:
+    NullEventQueue() { }
+    virtual ~NullEventQueue() { }
+    virtual bool enqueueEvent(PassRefPtrWillBeRawPtr<Event>) OVERRIDE { return true; }
+    virtual bool cancelEvent(Event*) OVERRIDE { return true; }
+    virtual void close() OVERRIDE { }
+};
+
+} // namespace
+
+NullExecutionContext::NullExecutionContext()
+    : m_tasksNeedSuspension(false)
+    , m_queue(adoptPtrWillBeNoop(new NullEventQueue()))
+{
+}
+
+} // namespace WebCore