Reland: mus: Enable system modal windows

components/mus/ws/event_dispatcher.h

Index: components/mus/ws/event_dispatcher.h
diff --git a/components/mus/ws/event_dispatcher.h b/components/mus/ws/event_dispatcher.h
index bc0e94832c224288af9565a74571462775fc9e03..aa547b8f8ec1069b26b91780cf58dbe06fd12453 100644
--- a/components/mus/ws/event_dispatcher.h
+++ b/components/mus/ws/event_dispatcher.h
@@ -7,6 +7,7 @@
 
 #include <stdint.h>
 
+#include <list>
 #include <map>
 #include <memory>
 
@@ -60,6 +61,20 @@ class EventDispatcher : public ServerWindowObserver {
   // (indicated by returning |false|).
   bool SetCaptureWindow(ServerWindow* capture_window, bool in_nonclient_area);
 
+  // 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 if |modal_window| is a visible modal window that blocks current
+  // capture window and if that's the case, releases the capture.
+  void ReleaseCaptureBlockedByModalWindow(const ServerWindow* modal_window);
+
+  // Checks if the current capture window is blocked by any visible modal window
+  // and if that's the case, releases the capture.
+  void ReleaseCaptureBlockedByAnyModalWindow();
+
   // Retrieves the ServerWindow of the last mouse move.
   ServerWindow* mouse_cursor_source_window() const {
     return mouse_cursor_source_window_;
@@ -81,6 +96,7 @@ class EventDispatcher : public ServerWindowObserver {
   void ProcessEvent(const ui::Event& event);
 
  private:
+  using ServerWindowList = std::list<ServerWindow*>;
   friend class test::EventDispatcherTestApi;
 
   // Keeps track of state associated with an active pointer.
@@ -148,15 +164,24 @@ class EventDispatcher : public ServerWindowObserver {
   // way we continue to eat events until the up/cancel is received.
   void CancelPointerEventsToTarget(ServerWindow* window);
 
-  // Returns true if we're currently an observer for |window|. We are an
-  // observer for a window if any pointer events are targeting it.
-  bool IsObservingWindow(ServerWindow* window);
+  // Used to observe a window. Can be called multiple times on a window. To
+  // unobserve a window, UnobserveWindow() should be called the same number of
+  // times.
+  void ObserveWindow(ServerWindow* winodw);
+  void UnobserveWindow(ServerWindow* winodw);
 
   // Returns an Accelerator bound to the specified code/flags, and of the
   // matching |phase|. Otherwise returns null.
   Accelerator* FindAccelerator(const ui::KeyEvent& event,
                                const mojom::AcceleratorPhase phase);
 
+  // Returns the system modal window that is visible and added/shown most
+  // recently, if any.
+  ServerWindow* GetActiveSystemModalWindow() const;
+
+  // Removes system modal window at the given iterator and unobserves it.
+  void RemoveSystemModalWindow(ServerWindowList::iterator it);
+
   // ServerWindowObserver:
   void OnWillChangeWindowHierarchy(ServerWindow* window,
                                    ServerWindow* new_parent,
@@ -166,9 +191,13 @@ class EventDispatcher : public ServerWindowObserver {
 
   EventDispatcherDelegate* delegate_;
   ServerWindow* root_;
-  ServerWindow* capture_window_;
 
+  ServerWindow* capture_window_;
   bool capture_window_in_nonclient_area_;
+
+  // List of system modal windows in order they are added/shown.
+  ServerWindowList system_modal_windows_;
+
   bool mouse_button_down_;
   ServerWindow* mouse_cursor_source_window_;
 
@@ -188,6 +217,9 @@ class EventDispatcher : public ServerWindowObserver {
   // cancel or up.
   PointerIdToTargetMap pointer_targets_;
 
+  // Keeps track of number of observe requests for each observed window.
+  std::map<const ServerWindow*, uint8_t> observed_windows_;
+
   DISALLOW_COPY_AND_ASSIGN(EventDispatcher);
 };