Move lazy event dispatching code out of EventRouter.

extensions/browser/lazy_context_id.cc

+// Copyright 2017 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 "extensions/browser/lazy_context_id.h"
+
+#include "extensions/browser/lazy_background_task_queue.h"
+
+namespace extensions {
+
+LazyContextId::LazyContextId(content::BrowserContext* context,
+                             const ExtensionId& extension_id)
+    : type_(Type::kEventPage), context_(context), extension_id_(extension_id) {}
+
+LazyBackgroundTaskQueue* LazyContextId::GetTaskQueue() {
+  DCHECK(is_for_event_page());
+  return LazyBackgroundTaskQueue::Get(context_);
+}
+
+}  // namespace extensions