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diff --git a/chromium/components/mus/ws/modal_window_controller.h b/chromium/components/mus/ws/modal_window_controller.h
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+++ b/chromium/components/mus/ws/modal_window_controller.h
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+// Copyright 2016 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.
+
+#ifndef COMPONENTS_MUS_WS_MODAL_WINDOW_CONTROLLER_H_
+#define COMPONENTS_MUS_WS_MODAL_WINDOW_CONTROLLER_H_
+
+#include <list>
+#include <map>
+
+#include "components/mus/ws/server_window_drawn_tracker_observer.h"
+#include "components/mus/ws/server_window_observer.h"
+
+namespace mus {
+namespace ws {
+
+class EventDispatcher;
+class ServerWindow;
+class ServerWindowDrawnTracker;
+
+namespace test {
+class ModalWindowControllerTestApi;
+}
+
+// Used to keeps track of system modal windows and check whether windows are
+// blocked by modal windows or not to do appropriate retargetting of events.
+class ModalWindowController : public ServerWindowObserver,
+                              public ServerWindowDrawnTrackerObserver {
+ public:
+  explicit ModalWindowController(EventDispatcher* event_dispatcher);
+  ~ModalWindowController() override;
+
+  // Adds a system modal window. The window remains modal to system until it is
+  // destroyed. There can exist multiple system modal windows, in which case the
+  // one that is visible and added most recently or shown most recently would be
+  // the active one.
+  void AddSystemModalWindow(ServerWindow* window);
+
+  // Checks whether |modal_window| is a visible modal window that blocks
+  // |window|.
+  bool IsWindowBlockedBy(const ServerWindow* window,
+                         const ServerWindow* modal_window) const;
+
+  // Checks whether |window| is blocked by any visible modal window.
+  bool IsWindowBlocked(const ServerWindow* window) const;
+
+  // Returns the window that events targeted to |window| should be retargeted
+  // to; according to modal windows. If any modal window is blocking |window|
+  // (either system modal or window modal), returns the topmost one; otherwise,
+  // returns |window| itself.
+  const ServerWindow* GetTargetForWindow(const ServerWindow* window) const;
+  ServerWindow* GetTargetForWindow(ServerWindow* window) const {
+    return const_cast<ServerWindow*>(
+        GetTargetForWindow(static_cast<const ServerWindow*>(window)));
+  }
+
+ private:
+  friend class test::ModalWindowControllerTestApi;
+
+  // Returns the system modal window that is visible and added/shown most
+  // recently, if any.
+  ServerWindow* GetActiveSystemModalWindow() const;
+
+  // ServerWindowObserver:
+  void OnWindowDestroyed(ServerWindow* window) override;
+
+  // ServerWindowDrawnTrackerObserver:
+  void OnDrawnStateChanged(ServerWindow* ancestor,
+                           ServerWindow* window,
+                           bool is_drawn) override;
+
+  EventDispatcher* event_dispatcher_;
+
+  // List of system modal windows in order they are added/shown.
+  std::list<ServerWindow*> system_modal_windows_;
+
+  // Drawn trackers for system modal windows.
+  std::map<ServerWindow*, std::unique_ptr<ServerWindowDrawnTracker>>
+      window_drawn_trackers_;
+
+  DISALLOW_COPY_AND_ASSIGN(ModalWindowController);
+};
+
+}  // namespace ws
+}  // namespace mus
+
+#endif  // COMPONENTS_MUS_WS_MODAL_WINDOW_CONTROLLER_H_