Add --headless flag to Windows

headless/app/headless_shell_main.cc

Index: headless/app/headless_shell_main.cc
diff --git a/headless/app/headless_shell_main.cc b/headless/app/headless_shell_main.cc
index 3ae4553b06854f9745690e4cc992267a7e4862ad..5f63fcb9295c7337035d638479d86b8c260a4182 100644
--- a/headless/app/headless_shell_main.cc
+++ b/headless/app/headless_shell_main.cc
@@ -2,8 +2,20 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include "build/build_config.h"
 #include "headless/public/headless_shell.h"
 
+#if defined(OS_WIN)
+#include "content/public/app/sandbox_helper_win.h"
+#include "sandbox/win/src/sandbox_types.h"
+#endif
+
 int main(int argc, const char** argv) {
+#if defined(OS_WIN)
+  sandbox::SandboxInterfaceInfo sandbox_info = {0};
+  content::InitializeSandboxInfo(&sandbox_info);
+  return headless::HeadlessShellMain(0, &sandbox_info);
+#else
   return headless::HeadlessShellMain(argc, argv);
+#endif  // defined(OS_WIN)
 }