Content "gn check" work.

content/common/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/common/common.gni")
 import("//media/media_options.gni")
 import("//mojo/public/tools/bindings/mojom.gni")
 if (is_mac) {
@@ skipping 108 matching lines @@
       stubs_filename_root,
       "-p",
       "content/common/gpu/media",
     ]
 
     args += rebase_path(sources, root_build_dir)
   }
 }
 
 source_set("common") {
-  # Only the public target should depend on this. All other targets (even
-  # internal content ones) should depend on the public one.
-  visibility = [ "//content/public/common:common_sources" ]
+  # Targets external to content should always link to the public API.
+  # In addition, targets outside of the content component (shell and tests)
+  # must not link to this because it will duplicate the code in the component
+  # build.
+  visibility = [ "//content/*" ]
 
   sources = rebase_path(content_common_gypi_values.private_common_sources,
                         ".",
                         "//content")
 
   configs += [
     "//content:content_implementation",
     "//build/config:precompiled_headers",
     "//build/config/compiler:no_size_t_to_int_warning",
   ]
@@ skipping 46 matching lines @@
     "//skia",
     "//storage/common",
     "//third_party/WebKit/public:blink",
     "//third_party/boringssl",
     "//third_party/icu",
     "//third_party/libjingle",
     "//third_party/webrtc/base:rtc_base",
     "//ui/accessibility",
     "//ui/base",
     "//ui/base/ime",
-    "//ui/events/ipc:events_ipc",
+    "//ui/events/ipc",
     "//ui/gfx",
     "//ui/gfx/geometry",
     "//ui/gfx/ipc",
     "//ui/gl",
     "//ui/shell_dialogs",
     "//url",
     "//url/ipc:url_ipc",
   ]
 
   defines = []
@@ skipping 303 matching lines @@
     }
     if (is_android) {
       sources -= [
         "sandbox_linux/android/sandbox_bpf_base_policy_android.cc",
         "sandbox_linux/android/sandbox_bpf_base_policy_android.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 = [
+      ":common",
+    ]
+  }
+}
+
 mojom("mojo_bindings") {
+  # This interface is internal to content. However, this is not exported from
+  # the content component shared library. Code in content but outside of the
+  # content component (content/test or content/shell) should link to this
+  # directly.
+  visibility = [ "//content/*" ]
+
   sources = [
     "application_setup.mojom",
     "background_sync_service.mojom",
     "geolocation_service.mojom",
     "image_downloader/image_downloader.mojom",
     "leveldb_wrapper.mojom",
     "permission_service.mojom",
     "presentation/presentation_service.mojom",
     "process_control.mojom",
     "render_frame_setup.mojom",
@@ skipping 13 matching lines @@
     "//components/leveldb/public/interfaces",
     "//components/mus/public/interfaces",
     "//content/public/common:mojo_bindings",
     "//mojo/shell/public/interfaces",
     "//skia/public/interfaces",
     "//third_party/WebKit/public:mojo_bindings",
     "//ui/mojo/geometry:interfaces",
     "//url/mojo:url_mojom_origin",
   ]
 }