Content "gn check" work.

content/child/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("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//content/child/child.gni")
 
 source_set("child") {
-  # Only the public target should depend on this. All other targets (even
-  # internal content ones) should depend on the public one.
-  visibility = [ "//content/public/child:child_sources" ]
+  # Targets external to content should always link to the public API.
+  # Internal targets can link to this but only if they're child processes
+  # (i.e. not content/browser or content/common) and only if they're inside the
+  # content component (i.e. not content/test or content/shell).
+  visibility = [
+    "//content/gpu/*",
+    "//content/plugin/*",
+    "//content/ppapi_plugin/*",
+    "//content/public/child:child_sources",
+    "//content/renderer/*",
+    "//content/utility/*",
+  ]
 
   sources = rebase_path(content_child_gypi_values.private_child_sources,
                         ".",
                         "//content")
 
   configs += [
     "//build/config:precompiled_headers",
     "//content/public/common:mojo_shell_client",
   ]
 
@@ skipping 86 matching lines @@
 
   if (use_aura && is_mac) {
     # This file is already excluded on non-Mac.
     sources -= [ "npapi/webplugin_delegate_impl_mac.mm" ]
   }
 
   if (is_win || !use_aura) {
     sources -= [ "npapi/webplugin_delegate_impl_aura.cc" ]
   }
 }