Make chrome GN build work in component mode.

content/public/utility/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.
 
-source_set("utility") {
+# See //content/BUILD.gn for how this works.
+group("utility") {
+  if (is_component_build) {
+    deps = [ "//content" ]
+  } else {
+    deps = [ ":utility_sources" ]
+  }
+  forward_dependent_configs_from = deps
+}
+
+source_set("utility_sources") {
+  visibility = [ "//content/*" ]
+
   sources = [
     "content_utility_client.cc",
     "content_utility_client.h",
     "utility_thread.cc",
     "utility_thread.h",
   ]
 
   configs += [ "//content:content_implementation" ]
 
   deps = [
     "//base",
     "//content:export",
-    "//content/public/common",
+    "//content/public/common:common_sources",
     "//content/utility",
     "//ipc",
   ]
 
   allow_circular_includes_from = [
     # This target is a pair with content/browser. They always go together and
     # include headers from each other.
-    "//content/utility",
+    # TODO(brettw) enable this when this permits non-dependent targets.
+    #"//content/utility",
   ]
 }