Do not try to link chrome or app_shell in chromeos gn build.

extensions/shell/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("//tools/grit/grit_rule.gni")
 
 assert(enable_extensions)
 
 grit("resources") {
   source = "app_shell_resources.grd"
@@ skipping 109 matching lines @@
   ]
   if (is_chromeos) {
     deps += [
       "//chromeos",
       "//ui/chromeos:ui_chromeos",
       "//ui/display",
     ]
   }
 }
 
-executable("app_shell") {
-  # testonly because :app_shell_lib is testonly. See :app_shell_lib comment.
-  testonly = true
-  deps = [
-    ":app_shell_lib",
-    "//extensions:shell_and_test_pak",
-  ]
-  sources = [ "app/shell_main.cc" ]
+if (!is_chromeos) {
+    executable("app_shell") {
+    # testonly because :app_shell_lib is testonly. See :app_shell_lib comment.
+    testonly = true
+    deps = [
+        ":app_shell_lib",
+        "//extensions:shell_and_test_pak",
+    ]
+    sources = [ "app/shell_main.cc" ]
+    }
 }
 
 action("version_header") {
   script = "//build/util/version.py"
   version_path = "//chrome/VERSION"
   lastchange_path = "//build/util/LASTCHANGE"
   version_h = "common/version.h.in"
   version_full = exec_script(
     script,
     ["-f", rebase_path(version_path, root_build_dir),
      "-t", "@MAJOR@.@MINOR@.@BUILD@.@PATCH@"],
     "trim string",
     ["VERSION"])
   inputs = [
     lastchange_path,
     version_path,
     version_h
   ]
   outputs = [ "$target_gen_dir/common/version.h" ]
   args = [
     "-f", rebase_path(lastchange_path, root_build_dir),
     "-e", "VERSION_FULL=\"$version_full\"",
     rebase_path(version_h, root_build_dir),
     rebase_path("$target_gen_dir/common/version.h")
   ]
 }