Content "gn check" work.

content/browser/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/browser/browser.gni")
 import("//media/media_options.gni")
 import("//mojo/public/mojo_application_manifest.gni")
 
 source_set("browser") {
   # Only the public target should depend on this. All other targets (even
   # internal content ones) should depend on the public one.
-  visibility = [ "//content/public/browser:browser_sources" ]
+  visibility = [
+    ":for_content_tests",
+    "//content/public/browser:browser_sources",
+  ]
 
   configs += [
     "//build/config:precompiled_headers",
     "//content:content_implementation",
     "//content/public/common:mojo_shell_client",
     "//third_party/WebKit/public:debug_devtools",
     "//v8:external_startup_data",
   ]
   defines = []
   libs = []
@@ skipping 494 matching lines @@
   if (enable_webvr && is_android) {
     sources += [
       "vr/android/cardboard/cardboard_vr_device.cc",
       "vr/android/cardboard/cardboard_vr_device.h",
       "vr/android/cardboard/cardboard_vr_device_provider.cc",
       "vr/android/cardboard/cardboard_vr_device_provider.h",
     ]
   }
 }
 
+# See comment at the top of //content/BUILD.gn for how this works.
+group("for_content_tests") {
+  visibility = [ "//content/test/*" ]
+  if (!is_component_build) {
+    public_deps = [
+      ":browser",
+    ]
+  }
+}
+
 mojo_application_manifest("chrome_manifest") {
   type = "exe"
   application_name = "chrome"
   source = "mojo/chrome_manifest.json"
 }
 
 mojo_application_manifest("chrome_renderer_manifest") {
   type = "exe"
   application_name = "chrome_renderer"
   source = "mojo/chrome_renderer_manifest.json"
 }