mus: Add PointerWatcher for passively observing mouse and touch events

components/mus/public/cpp/window_tree_connection.h

Index: components/mus/public/cpp/window_tree_connection.h
diff --git a/components/mus/public/cpp/window_tree_connection.h b/components/mus/public/cpp/window_tree_connection.h
index daa2f682a8dd683c688fc25033fd7f2ab80e52b9..b4b235154b68b31d294e01f847a1478af457d3ad 100644
--- a/components/mus/public/cpp/window_tree_connection.h
+++ b/components/mus/public/cpp/window_tree_connection.h
@@ -12,6 +12,7 @@
 #include <vector>
 
 #include "components/mus/common/types.h"
+#include "components/mus/public/interfaces/input_event_constants.mojom.h"
 #include "components/mus/public/interfaces/window_tree.mojom.h"
 #include "mojo/public/cpp/bindings/interface_request.h"
 
@@ -77,6 +78,11 @@ class WindowTreeConnection {
   // Sets focus to null. This does nothing if focus is currently null.
   virtual void ClearFocus() = 0;
 
+  // See description in window_tree.mojom. When an existing event observer is
+  // updated or cleared then any future events from the server for that observer
+  // will be ignored.
+  virtual void SetEventObserver(mojom::EventMatcherPtr matcher) = 0;
+
   // Creates and returns a new Window (which is owned by the window server).
   // Windows are initially hidden, use SetVisible(true) to show.
   Window* NewWindow() { return NewWindow(nullptr); }