Enable building headless_shell in MAC. This is an initial implementation with a hidden window, rath…

headless/BUILD.gn

Index: headless/BUILD.gn
diff --git a/headless/BUILD.gn b/headless/BUILD.gn
index fc234f7e058986ca678f70c45b740ca195e9e98d..8b8c6a9a6e7ef7bd23dacb85d4cf966097dd1ae5 100644
--- a/headless/BUILD.gn
+++ b/headless/BUILD.gn
@@ -196,6 +196,7 @@ static_library("headless_lib") {
               "lib/browser/headless_browser_context_options.h",
               "lib/browser/headless_browser_impl.cc",
               "lib/browser/headless_browser_impl.h",
+              "lib/browser/headless_browser_impl_mac.mm",
               "lib/browser/headless_browser_main_parts.cc",
               "lib/browser/headless_browser_main_parts.h",
               "lib/browser/headless_content_browser_client.cc",
@@ -289,7 +290,6 @@ static_library("headless_lib") {
     "//net",
     "//services/service_manager/public/cpp",
     "//third_party/mesa:osmesa",
-    "//ui/aura",
     "//ui/base",
     "//ui/compositor",
     "//ui/display",
@@ -305,6 +305,10 @@ static_library("headless_lib") {
     ]
   }
 
+  if (!is_mac) {
+    deps += [ "//ui/aura" ]
+  }
+
   if (headless_use_embedded_resources) {
     deps += [ ":embed_resources" ]
     sources += [