mus: Add watcher for all touch events.

services/ui/ws/window_tree.h

Index: services/ui/ws/window_tree.h
diff --git a/services/ui/ws/window_tree.h b/services/ui/ws/window_tree.h
index c975b06e0d61f82010c5c70599b19d540a1528c8..fd73bf3c8bb16403f8fb7ba7a415c356b8fe144a 100644
--- a/services/ui/ws/window_tree.h
+++ b/services/ui/ws/window_tree.h
@@ -360,8 +360,9 @@ class WindowTree : public mojom::WindowTree,
       override;
   void SetCapture(uint32_t change_id, Id window_id) override;
   void ReleaseCapture(uint32_t change_id, Id window_id) override;
-  void SetEventObserver(mojom::EventMatcherPtr matcher,
+  void AddEventObserver(mojom::EventMatcherPtr matcher,
                         uint32_t observer_id) override;
+  void RemoveEventObserver(uint32_t observer_id) override;
   void SetWindowBounds(uint32_t change_id,
                        Id window_id,
                        const gfx::Rect& bounds) override;
@@ -472,12 +473,10 @@ class WindowTree : public mojom::WindowTree,
   // reasonable timeframe.
   bool janky_ = false;
 
-  // Set when the client is using SetEventObserver() to observe events,
-  // otherwise null.
-  std::unique_ptr<EventMatcher> event_observer_matcher_;
-
-  // The ID supplied by the client for the current event observer.
-  uint32_t event_observer_id_ = 0;
+  // Set when the client is using AddEventObserver() to observe events,
+  // otherwise null. Key is an ID supplied by the client for the
+  // event observer
+  std::map<uint32_t, std::unique_ptr<EventMatcher>> event_observer_matchers_;
 
   // WindowManager the current event came from.
   WindowManagerState* event_source_wms_ = nullptr;