Aura desktop: Really implement DesktopActivationClient::OnWillFocusWindow().

ui/aura/desktop/desktop_activation_client.cc

 // Copyright (c) 2012 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 "ui/aura/desktop/desktop_activation_client.h"
 
 #include "base/auto_reset.h"
 #include "ui/aura/client/activation_delegate.h"
 #include "ui/aura/focus_manager.h"
 #include "ui/aura/root_window.h"
@@ skipping 48 matching lines @@
   if (window == current_active_)
     current_active_ = NULL;
 }
 
 aura::Window* DesktopActivationClient::GetActiveWindow() {
   return current_active_;
 }
 
 bool DesktopActivationClient::OnWillFocusWindow(Window* window,
                                                 const Event* event) {
-  // TODO(erg): Is this OK? Logic is much more nuanced in ash.
-  return true;
+  return CanActivateWindow(window);
 }
 
 void DesktopActivationClient::OnWindowFocused(aura::Window* window) {
   ActivateWindow(GetActivatableWindow(window));
 }
 
 bool DesktopActivationClient::CanActivateWindow(aura::Window* window) const {
   return window &&
       window->IsVisible() &&
       (!aura::client::GetActivationDelegate(window) ||
@@ skipping 11 matching lines @@
     // that path instead.
     if (child->transient_parent())
       return GetActivatableWindow(child->transient_parent());
     parent = parent->parent();
     child = child->parent();
   }
   return NULL;
 }
 
 }  // namespace aura