Content "gn check" work.

content/browser/tracing/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("//tools/grit/grit_rule.gni")
 
 # generate_about_tracing puts its files in this directory
 tracing_gen_dir = "$root_gen_dir/content/browser/tracing"
 
 # The script just writes filename with no dirs to the .grd, so we always need
 # this file to be in the same directory as the inputs.
 tracing_grd = "$tracing_gen_dir/tracing_resources.grd"
 
 action("generate_tracing_grd") {
-  visibility = [ ":*" ]
+  visibility = [ ":*" ]  # Depend on ":resources" to get this.
   script = "generate_trace_viewer_grd.py"
 
   input_pages = [
     "$tracing_gen_dir/about_tracing.html",
     "$tracing_gen_dir/about_tracing.js",
   ]
   inputs = input_pages
   outputs = [
     tracing_grd,
   ]
@@ skipping 18 matching lines @@
   # resource_ids has an entry for our .grd file that looks like:
   # "<(SHARED_INTERMEDIATE_DIR)/content/browser/tracing/tracing_resources.grd"
   # and what we pass here should make that resolve to our .grd file.
   defines =
       [ "SHARED_INTERMEDIATE_DIR=" + rebase_path(root_gen_dir, root_build_dir) ]
 
   deps = [
     ":generate_tracing_grd",
   ]
 }