Content "gn check" work.

content/app/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/chrome_build.gni")
 
 content_app_sources = [
   "android/app_jni_registrar.cc",
   "android/app_jni_registrar.h",
   "android/child_process_service.cc",
@@ skipping 49 matching lines @@
 ]
 
 if (!is_multi_dll_chrome) {
   content_app_deps += [ "//content/gpu:gpu_sources" ]
 }
 
 # This includes the app sources for both the browser and child processes.
 source_set("both") {
   # Only the public target should depend on this. All other targets (even
   # internal content ones) should depend on the public one.
-  visibility = [ "//content/public/app:*" ]
+  visibility = [
+    ":both_for_content_tests",  # See top of //content/BUILD.gn for why.
+    "//content/public/app:*",
+  ]
 
   sources = content_app_sources
   configs += content_app_extra_configs
   deps = content_app_deps
 }
 
+# See comment at the top of //content/BUILD.gn for how this works.
+group("both_for_content_tests") {
+  visibility = [ "//content/test/*" ]
+  if (!is_component_build) {
+    public_deps = [
+      ":both",
+    ]
+  }
+}
+
 if (is_multi_dll_chrome) {
   # It doesn't make sense to do the browser/child dll split in component mode.
   assert(!is_component_build)
 
   source_set("browser") {
     visibility = [ "//content/public/app:browser" ]
 
     sources = content_app_sources
     configs += content_app_extra_configs
     deps = content_app_deps
 
     defines = [ "CHROME_MULTIPLE_DLL_BROWSER" ]
   }
 
   source_set("child") {
     visibility = [ "//content/public/app:child" ]
 
     sources = content_app_sources
     configs += content_app_extra_configs
     deps = content_app_deps
 
     defines = [ "CHROME_MULTIPLE_DLL_CHILD" ]
   }
 }