Minimize headless code that refers to aura.

headless/BUILD.gn

Index: headless/BUILD.gn
diff --git a/headless/BUILD.gn b/headless/BUILD.gn
index 7f155ee2e080e1c520781bb5822be8ac047a6ac9..c6e1a9d4ecf54a464d6e2e844da74e909cc1980b 100644
--- a/headless/BUILD.gn
+++ b/headless/BUILD.gn
@@ -169,16 +169,10 @@ static_library("headless_lib") {
               "lib/browser/headless_devtools_manager_delegate.h",
               "lib/browser/headless_platform_event_source.cc",
               "lib/browser/headless_platform_event_source.h",
-              "lib/browser/headless_screen.cc",
-              "lib/browser/headless_screen.h",
               "lib/browser/headless_url_request_context_getter.cc",
               "lib/browser/headless_url_request_context_getter.h",
               "lib/browser/headless_web_contents_impl.cc",
               "lib/browser/headless_web_contents_impl.h",
-              "lib/browser/headless_window_parenting_client.cc",
-              "lib/browser/headless_window_parenting_client.h",
-              "lib/browser/headless_window_tree_host.cc",
-              "lib/browser/headless_window_tree_host.h",
               "lib/headless_content_client.cc",
               "lib/headless_content_client.h",
               "lib/headless_content_main_delegate.cc",
@@ -226,6 +220,18 @@ static_library("headless_lib") {
               "public/util/user_agent.h",
             ]
 
+  if (use_aura) {
+    sources += [
+      "lib/browser/headless_browser_impl_aura.cc",
+      "lib/browser/headless_screen.cc",
+      "lib/browser/headless_screen.h",
+      "lib/browser/headless_window_parenting_client.cc",
+      "lib/browser/headless_window_parenting_client.h",
+      "lib/browser/headless_window_tree_host.cc",
+      "lib/browser/headless_window_tree_host.h",
+    ]
+  }
+
   deps = [
     ":gen_devtools_client_api",
     ":pak",