Revert of Finish eliminating PlatformWindowMus

blimp/engine/app/ui/blimp_window_tree_host.cc

Index: blimp/engine/app/ui/blimp_window_tree_host.cc
diff --git a/blimp/engine/app/ui/blimp_window_tree_host.cc b/blimp/engine/app/ui/blimp_window_tree_host.cc
index a16d9c64e0652eccddd581667174985f01db99f0..9c38d5ddd89144f56e4bee9c565d5ec92b464176 100644
--- a/blimp/engine/app/ui/blimp_window_tree_host.cc
+++ b/blimp/engine/app/ui/blimp_window_tree_host.cc
@@ -5,15 +5,13 @@
 #include "blimp/engine/app/ui/blimp_window_tree_host.h"
 
 #include "base/memory/ptr_util.h"
-#include "ui/gfx/native_widget_types.h"
 #include "ui/platform_window/stub/stub_window.h"
 
 namespace blimp {
 namespace engine {
 
 BlimpWindowTreeHost::BlimpWindowTreeHost() : aura::WindowTreeHostPlatform() {
-  SetPlatformWindow(base::WrapUnique(
-      new ui::StubWindow(this, gfx::kNullAcceleratedWidget)));
+  SetPlatformWindow(base::WrapUnique(new ui::StubWindow(this)));
 }
 
 BlimpWindowTreeHost::~BlimpWindowTreeHost() {}