Add --headless flag to Windows

headless/lib/headless_content_main_delegate.h

Index: headless/lib/headless_content_main_delegate.h
diff --git a/headless/lib/headless_content_main_delegate.h b/headless/lib/headless_content_main_delegate.h
index 0aca886cbbe5eca36fb970bc2c372b25f84d3103..eb8cd61eea60bd0e3c5c3669861eec9c7f1a27f9 100644
--- a/headless/lib/headless_content_main_delegate.h
+++ b/headless/lib/headless_content_main_delegate.h
@@ -11,6 +11,8 @@
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "content/public/app/content_main_delegate.h"
+#include "content/public/browser/content_browser_client.h"
+#include "content/public/renderer/content_renderer_client.h"
 #include "headless/lib/browser/headless_platform_event_source.h"
 #include "headless/lib/headless_content_client.h"
 #include "headless/public/headless_export.h"
@@ -22,8 +24,6 @@ class CommandLine;
 namespace headless {
 
 class HeadlessBrowserImpl;
-class HeadlessContentBrowserClient;
-class HeadlessContentRendererClient;
 
 // Exported for tests.
 class HEADLESS_EXPORT HeadlessContentMainDelegate
@@ -57,8 +57,8 @@ class HEADLESS_EXPORT HeadlessContentMainDelegate
 
   static HeadlessContentMainDelegate* GetInstance();
 
-  std::unique_ptr<HeadlessContentBrowserClient> browser_client_;
-  std::unique_ptr<HeadlessContentRendererClient> renderer_client_;
+  std::unique_ptr<content::ContentRendererClient> renderer_client_;
+  std::unique_ptr<content::ContentBrowserClient> browser_client_;
   HeadlessContentClient content_client_;
   HeadlessPlatformEventSource platform_event_source_;