mus: Add EventObserver to allow passively listening to UI events

components/mus/ws/window_tree.cc

Index: components/mus/ws/window_tree.cc
diff --git a/components/mus/ws/window_tree.cc b/components/mus/ws/window_tree.cc
index 863a3a13e61a2095581b0f08fac3b089e39daa76..8ebe876acc0203f2a75fe8a8145fab4ee9c49787 100644
--- a/components/mus/ws/window_tree.cc
+++ b/components/mus/ws/window_tree.cc
@@ -13,6 +13,7 @@
 #include "components/mus/ws/default_access_policy.h"
 #include "components/mus/ws/display.h"
 #include "components/mus/ws/display_manager.h"
+#include "components/mus/ws/event_tester.h"
 #include "components/mus/ws/focus_controller.h"
 #include "components/mus/ws/operation.h"
 #include "components/mus/ws/platform_display.h"
@@ -956,6 +957,11 @@ void WindowTree::DispatchInputEventImpl(ServerWindow* target,
                                mojom::Event::From(event));
 }
 
+void WindowTree::SendToEventObserver(const ui::Event& event) {
+  if (event_observer_tester_ && event_observer_tester_->MatchesEvent(event))
+    client()->OnEventObserved(mojom::Event::From(event));

[sky, 2016/04/21 17:23:04]

If the event was targetted at this client, then I wouldn't sent it again.
Additionally don't send events to windowtrees of inactive users.

[James Cook, 2016/04/22 18:22:55]

Done.

+}
+
 void WindowTree::NewWindow(
     uint32_t change_id,
     Id transport_window_id,
@@ -1109,6 +1115,14 @@ void WindowTree::ReleaseCapture(uint32_t change_id, Id window_id) {
   client()->OnChangeCompleted(change_id, success);
 }
 
+void WindowTree::SetEventObserver(mojom::EventMatcherPtr matcher) {
+  event_observer_tester_.reset(new EventTester(*matcher));
+}
+
+void WindowTree::ClearEventObserver() {
+  event_observer_tester_.reset();
+}
+
 void WindowTree::SetWindowBounds(uint32_t change_id,
                                  Id window_id,
                                  mojo::RectPtr bounds) {