aura: Use PlatformWindow from WindowTreeHost.

ui/platform_window/win/win_window.cc

Index: ui/platform_window/win/win_window.cc
diff --git a/ui/platform_window/win/win_window.cc b/ui/platform_window/win/win_window.cc
index 11db5fcfa6fda1b0613f1ac82aa654ef42fb9133..89ff68382f4bf2302e763026e48025137ee3f6b3 100644
--- a/ui/platform_window/win/win_window.cc
+++ b/ui/platform_window/win/win_window.cc
@@ -13,6 +13,8 @@ namespace ui {
 
 namespace {
 
+bool use_popup_as_root_window_for_test = false;
+
 gfx::Rect GetWindowBoundsForClientBounds(DWORD style, DWORD ex_style,
                                          const gfx::Rect& bounds) {
   RECT wr;
@@ -37,6 +39,8 @@ WinWindow::WinWindow(PlatformWindowDelegate* delegate,
                      const gfx::Rect& bounds)
     : delegate_(delegate) {
   CHECK(delegate_);
+  if (use_popup_as_root_window_for_test)
+    set_window_style(WS_POPUP);
   gfx::Rect window_bounds = GetWindowBoundsForClientBounds(
       WS_OVERLAPPEDWINDOW, window_ex_style(), bounds);
   gfx::WindowImpl::Init(NULL, window_bounds);
@@ -126,6 +130,7 @@ LRESULT WinWindow::OnKeyEvent(UINT message, WPARAM w_param, LPARAM l_param) {
 }
 
 LRESULT WinWindow::OnNCActivate(UINT message, WPARAM w_param, LPARAM l_param) {
+  delegate_->OnActivationChanged(!!w_param);
   return DefWindowProc(hwnd(), message, w_param, l_param);
 }
 
@@ -162,4 +167,12 @@ void WinWindow::OnWindowPosChanged(WINDOWPOS* window_pos) {
   }
 }
 
+namespace test {
+
+// static
+void SetUsePopupAsRootWindowForTest(bool use) {
+  use_popup_as_root_window_for_test = use;
+}
+
+}  // namespace test
 }  // namespace ui