Add IDL and initial Blink API for Background Sync

Source/modules/background_sync/SyncEvent.cpp

+// Copyright 2015 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 "modules/background_sync/SyncEvent.h"
+
+namespace blink {
+
+SyncEvent::SyncEvent()
+{
+}
+
+SyncEvent::SyncEvent(const AtomicString& type, SyncRegistration* syncRegistration, WaitUntilObserver* observer)
+    : ExtendableEvent(type, ExtendableEventInit(), observer)
+    , m_syncRegistration(syncRegistration)
+{
+}
+
+SyncEvent::SyncEvent(const AtomicString& type, const SyncEventInit& init)
+    : ExtendableEvent(type, init)
+{
+    m_syncRegistration = init.registration();
+}
+
+SyncEvent::~SyncEvent()
+{
+}
+
+const AtomicString& SyncEvent::interfaceName() const
+{
+    return EventNames::SyncEvent;
+}
+
+SyncRegistration* SyncEvent::registration()
+{
+    return m_syncRegistration.get();
+}
+
+DEFINE_TRACE(SyncEvent)
+{
+    visitor->trace(m_syncRegistration);
+    ExtendableEvent::trace(visitor);
+}
+
+} // namespace blink