Make chrome GN build work in component mode.

content/gpu/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/ui.gni")
 import("//content/content.gni")
 
 source_set("gpu") {
-  # TODO(brettw) it seems like this should be only visible to content like
-  # the other non-public content directories are. But this is depended on by
-  # the chrome target.
+  visibility = [ "//content/*" ]
 
   sources = [
     "gpu_main.cc",
     "gpu_process.cc",
     "gpu_process.h",
     "gpu_child_thread.cc",
     "gpu_child_thread.h",
     "gpu_watchdog_thread.cc",
     "gpu_watchdog_thread.h",
     "in_process_gpu_thread.cc",
@@ skipping 23 matching lines @@
   }
 
   if (is_chromeos && cpu_arch != "arm") {
     configs += [ "//third_party/libva:libva_config" ]
   }
 
   if (use_x11) {
     deps += [ "//ui/events/platform/x11" ]
   }
 }