Move lazy event dispatching code out of EventRouter.

extensions/browser/BUILD.gn

Index: extensions/browser/BUILD.gn
diff --git a/extensions/browser/BUILD.gn b/extensions/browser/BUILD.gn
index 46315eaa79a5defe6546ad04a4e5d77956c05722..4cc35d14629f194cbb636d3816bfc83dc93431ca 100644
--- a/extensions/browser/BUILD.gn
+++ b/extensions/browser/BUILD.gn
@@ -88,6 +88,8 @@ source_set("browser_sources") {
     "event_router_factory.h",
     "events/lazy_event_dispatch_util.cc",
     "events/lazy_event_dispatch_util.h",
+    "events/lazy_event_dispatcher.cc",
+    "events/lazy_event_dispatcher.h",
     "extension_api_frame_id_map.cc",
     "extension_api_frame_id_map.h",
     "extension_dialog_auto_confirm.cc",
@@ -233,6 +235,8 @@ source_set("browser_sources") {
     "lazy_background_task_queue.h",
     "lazy_background_task_queue_factory.cc",
     "lazy_background_task_queue_factory.h",
+    "lazy_context_id.cc",
+    "lazy_context_id.h",
     "load_monitoring_extension_host_queue.cc",
     "load_monitoring_extension_host_queue.h",
     "management_policy.cc",