Add missing .h files to .gn files that have a .cc file next to it in the gn file already.

extensions/renderer/BUILD.gn

 # 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.
 
 import("//build/config/features.gni")
 import("//extensions/features/features.gni")
 
 assert(enable_extensions)
 
 source_set("renderer") {
@@ skipping 107 matching lines @@
     "native_extension_bindings_system.h",
     "native_handler.cc",
     "native_handler.h",
     "object_backed_native_handler.cc",
     "object_backed_native_handler.h",
     "process_info_native_handler.cc",
     "process_info_native_handler.h",
     "programmatic_script_injector.cc",
     "programmatic_script_injector.h",
     "render_frame_observer_natives.cc",
+    "render_frame_observer_natives.h",
     "renderer_extension_registry.cc",
     "renderer_extension_registry.h",
     "request_sender.cc",
     "request_sender.h",
     "resource_bundle_source_map.cc",
     "resource_bundle_source_map.h",
     "resources/app_runtime_custom_bindings.js",
     "resources/app_window_custom_bindings.js",
     "resources/binding.js",
     "resources/context_menus_custom_bindings.js",
@@ skipping 208 matching lines @@
     "//ui/base",
   ]
 
   if (enable_wifi_display && proprietary_codecs) {
     sources += [
       "api/display_source/wifi_display/wifi_display_elementary_stream_descriptor_unittest.cc",
       "api/display_source/wifi_display/wifi_display_media_packetizer_unittest.cc",
     ]
   }
 }