Minimize headless code that refers to aura.

headless/lib/browser/headless_browser_impl.cc

Index: headless/lib/browser/headless_browser_impl.cc
diff --git a/headless/lib/browser/headless_browser_impl.cc b/headless/lib/browser/headless_browser_impl.cc
index 93d6918a76c8d022a1f46f57296f2c8f5da45f1a..0154a84f4e6a486d83fbd7937f7b88ee8d9bae2d 100644
--- a/headless/lib/browser/headless_browser_impl.cc
+++ b/headless/lib/browser/headless_browser_impl.cc
@@ -18,7 +18,6 @@
 #include "headless/lib/browser/headless_browser_context_impl.h"
 #include "headless/lib/browser/headless_browser_main_parts.h"
 #include "headless/lib/browser/headless_web_contents_impl.h"
-#include "headless/lib/browser/headless_window_parenting_client.h"
 #include "headless/lib/browser/headless_window_tree_host.h"
 #include "headless/lib/headless_content_main_delegate.h"
 #include "ui/aura/env.h"
@@ -121,17 +120,7 @@ void HeadlessBrowserImpl::set_browser_main_parts(
 }
 
 void HeadlessBrowserImpl::RunOnStartCallback() {
-  DCHECK(aura::Env::GetInstance());
-  ui::DeviceDataManager::CreateInstance();
-
-  window_tree_host_.reset(
-      new HeadlessWindowTreeHost(gfx::Rect(options()->window_size)));
-  window_tree_host_->InitHost();
-  window_tree_host_->window()->Show();
-
-  window_parenting_client_.reset(
-      new HeadlessWindowParentingClient(window_tree_host_->window()));
-
+  PlatformCreateWindow();
   on_start_callback_.Run(this);
   on_start_callback_ = base::Callback<void(HeadlessBrowser*)>();
 }
@@ -179,7 +168,7 @@ base::WeakPtr<HeadlessBrowserImpl> HeadlessBrowserImpl::GetWeakPtr() {
   return weak_ptr_factory_.GetWeakPtr();
 }
 
-aura::WindowTreeHost* HeadlessBrowserImpl::window_tree_host() const {
+HeadlessWindowTreeHost* HeadlessBrowserImpl::window_tree_host() const {
   return window_tree_host_.get();
 }