[Mac/GN] Add a BUILD.gn file for //chrome/app_shim.

chrome/app_shim/BUILD.gn

Index: chrome/app_shim/BUILD.gn
diff --git a/chrome/app_shim/BUILD.gn b/chrome/app_shim/BUILD.gn
index 74bca935118768c42fd0df65d50564c7b38d9f94..141bf72bef0ac601c376752a56e564b9163001a4 100644
--- a/chrome/app_shim/BUILD.gn
+++ b/chrome/app_shim/BUILD.gn
@@ -2,6 +2,8 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build/config/mac/rules.gni")
+
 # This is the part of the shim process compiled into Chrome. It runs only
 # in the shim process, after the shim finds and loads the Chrome
 # Framework bundle.
@@ -15,3 +17,24 @@ source_set("app_shim") {
     "//chrome/common:app_mode_app_support",
   ]
 }
+
+mac_app_bundle("app_mode_loader") {
+  extra_configs = [ "//build/config/compiler:wexit_time_destructors" ]
+
+  info_plist = "app_mode-Info.plist"
+
+  sources = [
+    "app_mode_loader_mac.mm",
+  ]
+
+  deps = [
+    "//chrome/common:app_mode_app_support",
+  ]
+
+  # TODO(rsesek): extra_substitutions = [ APP_MODE_APP_BUNDLE_ID ... ]
+
+  libs = [
+    "CoreFoundation.framework",
+    "Foundation.framework",
+  ]
+}