Add chrome/browser/apps/BUILD.gn and move Chrome-specific code there

chrome/browser/extensions/BUILD.gn

Index: chrome/browser/extensions/BUILD.gn
diff --git a/chrome/browser/extensions/BUILD.gn b/chrome/browser/extensions/BUILD.gn
index 8846ef9d4da1e5f2c2fd70c63a731ee78c65f1c6..c16e8fd57eb796d15175224e2832b0b9389635ac 100644
--- a/chrome/browser/extensions/BUILD.gn
+++ b/chrome/browser/extensions/BUILD.gn
@@ -15,18 +15,6 @@ static_library("extensions") {
   sources = [
     # TODO These references to files in //chrome/browser/ should either be
     # moved to the browser target or the files moved to this directory.
-    "../apps/app_launch_for_metro_restart_win.cc",
-    "../apps/app_launch_for_metro_restart_win.h",
-    "../apps/app_url_redirector.cc",
-    "../apps/app_url_redirector.h",
-    "../apps/app_window_registry_util.cc",
-    "../apps/app_window_registry_util.h",
-    "../apps/install_chrome_app.cc",
-    "../apps/install_chrome_app.h",
-    "../apps/shortcut_manager.cc",
-    "../apps/shortcut_manager.h",
-    "../apps/shortcut_manager_factory.cc",
-    "../apps/shortcut_manager_factory.h",
     "../ui/app_icon_loader.cc",
     "../ui/app_icon_loader.h",
     "../ui/toolbar/toolbar_actions_model.cc",
@@ -812,6 +800,7 @@ static_library("extensions") {
     "//content/public/browser",
   ]
   deps = [
+    "//apps",
     "//chrome:extra_resources",
     "//chrome:resources",
     "//chrome:strings",