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

build/config/BUILDCONFIG.gn

 # Copyright (c) 2013 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.
 
 # =============================================================================
 # BUILD FLAGS
 # =============================================================================
 #
 # This block lists input arguments to the build, along with their default
 # values. GN requires listing them explicitly so it can validate input and have
@@ skipping 14 matching lines @@
   #   -1 means auto-set (off in release, regular in debug).
   symbol_level = -1
 
   # Component build.
   is_component_build = false
   # Debug build.
   is_debug = true
 
   # Set to true when compiling with the Clang compiler. Typically this is used
   # to configure warnings.
-  is_clang = (os == "mac" || os == "ios" || os == "linux")
+  is_clang = (os == "mac" || os == "ios" || os == "linux" || os == "chromeos")
 
   # Forces a 64-bit build on Windows. Does nothing on other platforms. Normally
   # we build 32-bit on Windows regardless of the current host OS bit depth.
   # Setting this flag will override this logic and generate 64-bit toolchains.
   #
   # Normally this would get set automatically when you specify a target using
   # the 64-bit toolchain. You can also set this on the command line to convert
   # the default toolchain to 64-bit.
   force_win64 = false
 
@@ skipping 670 matching lines @@
       if (defined(invoker.output_extension)) { output_extension = invoker.output_extension }
       if (defined(invoker.output_name)) { output_name = invoker.output_name }
       if (defined(invoker.public)) { public = invoker.public }
       if (defined(invoker.public_configs)) { public_configs = invoker.public_configs }
       if (defined(invoker.public_deps)) { public_deps = invoker.public_deps }
       if (defined(invoker.sources)) { sources = invoker.sources }
       if (defined(invoker.visibility)) { visibility = invoker.visibility }
     }
   }
 }