Add a chrome://webapks page.

chrome/browser/ui/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/chromecast_build.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//build/split_static_library.gni")
 import("//chrome/common/features.gni")
@@ skipping 2252 matching lines @@
       "webui/offline/offline_internals_ui.cc",
       "webui/offline/offline_internals_ui.h",
       "webui/offline/offline_internals_ui_message_handler.cc",
       "webui/offline/offline_internals_ui_message_handler.h",
       "webui/popular_sites_internals_ui.cc",
       "webui/popular_sites_internals_ui.h",
       "webui/snippets_internals_message_handler.cc",
       "webui/snippets_internals_message_handler.h",
       "webui/snippets_internals_ui.cc",
       "webui/snippets_internals_ui.h",
+      "webui/webapks_handler.cc",
+      "webui/webapks_handler.h",
+      "webui/webapks_ui.cc",
+      "webui/webapks_ui.h",
     ]
     if (enable_vr_shell || enable_webvr) {
       if (enable_vr_shell) {
         defines += [ "ENABLE_VR_SHELL" ]
       }
       sources += [
         "webui/vr_shell/vr_shell_ui_message_handler.cc",
         "webui/vr_shell/vr_shell_ui_message_handler.h",
         "webui/vr_shell/vr_shell_ui_ui.cc",
         "webui/vr_shell/vr_shell_ui_ui.h",
@@ skipping 1213 matching lines @@
       "test/test_confirm_bubble_model.cc",
       "test/test_confirm_bubble_model.h",
     ]
     deps += [ "//chrome/test:test_support_ui" ]
   }
 
   if (enable_extensions) {
     deps += [ "//extensions/browser" ]
   }
 }