Make --headless flag work on Mac

headless/lib/browser/headless_content_browser_client.cc

 // Copyright 2015 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.
 
 #include "headless/lib/browser/headless_content_browser_client.h"
 
 #include <memory>
 #include <unordered_set>
 
 #include "base/base_switches.h"
@@ skipping 10 matching lines @@
 #include "content/public/common/content_switches.h"
 #include "content/public/common/service_names.mojom.h"
 #include "headless/grit/headless_lib_resources.h"
 #include "headless/lib/browser/headless_browser_context_impl.h"
 #include "headless/lib/browser/headless_browser_impl.h"
 #include "headless/lib/browser/headless_browser_main_parts.h"
 #include "headless/lib/browser/headless_devtools_manager_delegate.h"
 #include "headless/lib/headless_macros.h"
 #include "storage/browser/quota/quota_settings.h"
 #include "ui/base/resource/resource_bundle.h"
+#include "ui/gfx/switches.h"
 
 #if defined(HEADLESS_USE_BREAKPAD)
 #include "base/debug/leak_annotations.h"
 #include "components/crash/content/app/breakpad_linux.h"
 #include "components/crash/content/browser/crash_handler_host_linux.h"
 #include "content/public/common/content_descriptors.h"
 #endif  // defined(HEADLESS_USE_BREAKPAD)
 
 namespace headless {
 
@@ skipping 138 matching lines @@
   int crash_signal_fd = GetCrashSignalFD(command_line, *browser_->options());
   if (crash_signal_fd >= 0)
     mappings->Share(kCrashDumpSignal, crash_signal_fd);
 #endif  // defined(HEADLESS_USE_BREAKPAD)
 }
 #endif  // defined(OS_POSIX) && !defined(OS_MACOSX)
 
 void HeadlessContentBrowserClient::AppendExtraCommandLineSwitches(
     base::CommandLine* command_line,
     int child_process_id) {
+  command_line->AppendSwitch(switches::kHeadless);
 #if defined(HEADLESS_USE_BREAKPAD)
   // This flag tells child processes to also turn on crash reporting.
   if (breakpad::IsCrashReporterEnabled())
     command_line->AppendSwitch(switches::kEnableCrashReporter);
 #endif  // defined(HEADLESS_USE_BREAKPAD)
 }
 
 }  // namespace headless