Fix Fuchsia GN build.

BUILD.gn

 # Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 # This target will be built if no target is specified when invoking ninja.
 group("default") {
   if (defined(is_fuchsia) && (is_fuchsia || is_fuchsia_host)) {
     # Fuchsia has run_vm_tests marked testonly.
     testonly = true
   }
@@ skipping 28 matching lines @@
     "runtime/bin:dart_bootstrap($host_toolchain)",
     "runtime/bin:process_test",
     "runtime/bin:run_vm_tests",
     "runtime/bin:sample_extension",
     "runtime/bin:test_extension",
     "runtime/vm:patched_sdk",
   ]
 }
 
 group("runtime_kernel") {
+  if (defined(is_fuchsia) && (is_fuchsia || is_fuchsia_host)) {
+    # Fuchsia has run_vm_tests marked testonly.
+    testonly = true
+  }
   deps = [
     ":runtime",
 
     # TODO(rmacnak): Link this into 'dart'
     "utils/kernel-service:kernel-service",
   ]
 }
 
 group("runtime_precompiled") {
   deps = [
@@ skipping 186 matching lines @@
         rebase_path(input),
         "--output-file",
         rebase_path(output),
         "--build-id-map",
         rebase_path("$target_gen_dir/build_id_map"),
         "--compress",
       ]
     }
   }
 }