ui: Cleanup class/struct forward declarations

extensions/renderer/BUILD.gn

Index: extensions/renderer/BUILD.gn
diff --git a/extensions/renderer/BUILD.gn b/extensions/renderer/BUILD.gn
index 161d9d6860f4179cd2c6c9dfebf2d923f17c8b1d..0b7305d2e4faa819bccb357e94bdc481dd666231 100644
--- a/extensions/renderer/BUILD.gn
+++ b/extensions/renderer/BUILD.gn
@@ -18,10 +18,13 @@ source_set("renderer") {
     "api_activity_logger.h",
     "api_binding.cc",
     "api_binding.h",
+    "api_binding_types.h",
     "api_bindings_system.cc",
     "api_bindings_system.h",
     "api_definitions_natives.cc",
     "api_definitions_natives.h",
+    "api_event_handler.cc",
+    "api_event_handler.h",
     "api_request_handler.cc",
     "api_request_handler.h",
     "app_window_custom_bindings.cc",
@@ -51,6 +54,8 @@ source_set("renderer") {
     "dom_activity_logger.h",
     "event_bindings.cc",
     "event_bindings.h",
+    "event_emitter.cc",
+    "event_emitter.h",
     "extension_frame_helper.cc",
     "extension_frame_helper.h",
     "extension_groups.h",
@@ -264,6 +269,7 @@ source_set("unit_tests") {
     "api_binding_test_util.h",
     "api_binding_unittest.cc",
     "api_bindings_system_unittest.cc",
+    "api_event_handler_unittest.cc",
     "api_request_handler_unittest.cc",
     "api_test_base.cc",
     "api_test_base.h",