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

extensions/browser/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")
 
 group("browser") {
   public_deps = [
     "//extensions/browser:browser_context_keyed_service_factories",
@@ skipping 384 matching lines @@
     "api/cast_channel/keep_alive_delegate_unittest.cc",
     "api/cast_channel/logger_unittest.cc",
     "api/declarative/declarative_rule_unittest.cc",
     "api/declarative/deduping_factory_unittest.cc",
     "api/declarative/rules_registry_unittest.cc",
     "api/declarative_webrequest/webrequest_condition_attribute_unittest.cc",
     "api/declarative_webrequest/webrequest_condition_unittest.cc",
     "api/document_scan/document_scan_api_unittest.cc",
     "api/document_scan/document_scan_interface_chromeos_unittest.cc",
     "api/document_scan/mock_document_scan_interface.cc",
+    "api/document_scan/mock_document_scan_interface.h",
     "api/file_handlers/app_file_handler_util_unittest.cc",
     "api/file_handlers/directory_util_unittest.cc",
     "api/file_handlers/mime_util_unittest.cc",
     "api/idle/idle_api_unittest.cc",
     "api/mime_handler_private/mime_handler_private_unittest.cc",
     "api/networking_config/networking_config_service_chromeos_unittest.cc",
     "api/networking_private/networking_private_chromeos_unittest.cc",
     "api/power/power_api_unittest.cc",
     "api/runtime/restart_after_delay_api_unittest.cc",
     "api/sockets_tcp/sockets_tcp_api_unittest.cc",
@@ skipping 75 matching lines @@
     "//net:test_support",
     "//third_party/leveldatabase",
     "//third_party/zlib:zip",
   ]
 
   if (is_chromeos) {
     sources += [ "api/webcam_private/visca_webcam_unittest.cc" ]
     deps += [ "//chromeos:test_support" ]
   }
 }