[Aura] Support always-on-top top level window.

views/widget/native_widget_aura.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "views/widget/native_widget_aura.h"
 
 #include "base/bind.h"
 #include "ui/aura/desktop.h"
 #include "ui/aura/event.h"
 #include "ui/aura/window.h"
@@ skipping 68 matching lines @@
   window_->Init(params.create_texture_for_layer ?
                 ui::Layer::LAYER_HAS_TEXTURE : ui::Layer::LAYER_HAS_NO_TEXTURE);
   // TODO(beng): respect |params| authoritah wrt transparency.
   window_->layer()->SetFillsBoundsOpaquely(false);
   delegate_->OnNativeWidgetCreated();
   window_->set_minimum_size(delegate_->GetMinimumSize());
   window_->SetBounds(params.bounds);
   if (params.type == Widget::InitParams::TYPE_CONTROL) {
     window_->SetParent(params.GetParent());
   } else {
+    if (params.keep_on_top)
+      SetAlwaysOnTop(true);
     window_->SetParent(NULL);
     gfx::NativeView parent = params.GetParent();
     if (parent)
       parent->AddTransientChild(window_);
   }
   // TODO(beng): do this some other way.
   delegate_->OnNativeWidgetSizeChanged(params.bounds.size());
   can_activate_ = params.can_activate;
   if (params.type != Widget::InitParams::TYPE_TOOLTIP && !params.child) {
     DCHECK(GetWidget()->GetRootView());
@@ skipping 249 matching lines @@
 
 void NativeWidgetAura::Deactivate() {
   window_->Deactivate();
 }
 
 bool NativeWidgetAura::IsActive() const {
   return aura::Desktop::GetInstance()->active_window() == window_;
 }
 
 void NativeWidgetAura::SetAlwaysOnTop(bool on_top) {
-  NOTIMPLEMENTED();
+  SetNativeWindowProperty(aura::Window::kPropAlwaysOnTop,
+      reinterpret_cast<void*>(on_top));
+  // TODO(xiyuan): Switch containers if window_ is added to desktop already.
 }
 
 void NativeWidgetAura::Maximize() {
   window_->Maximize();
 }
 
 void NativeWidgetAura::Minimize() {
   NOTIMPLEMENTED();
 }
 
@@ skipping 277 matching lines @@
 }
 
 // static
 bool NativeWidgetPrivate::IsMouseButtonDown() {
   NOTIMPLEMENTED();
   return false;
 }
 
 }  // namespace internal
 }  // namespace views