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

extensions/shell/BUILD.gn

Index: extensions/shell/BUILD.gn
diff --git a/extensions/shell/BUILD.gn b/extensions/shell/BUILD.gn
index b667ba1c7682c98b3beb0830f3334b5634d67286..2861ae4981c4c4d522bec49bff4f7ddb16467f2a 100644
--- a/extensions/shell/BUILD.gn
+++ b/extensions/shell/BUILD.gn
@@ -127,14 +127,16 @@ source_set("app_shell_lib") {
   }
 }
 
-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") {