ozone: Map TouchEvent::touch_id_ into expected range

ui/aura/window_event_dispatcher.cc

Index: ui/aura/window_event_dispatcher.cc
diff --git a/ui/aura/window_event_dispatcher.cc b/ui/aura/window_event_dispatcher.cc
index 8b7db5d1eb1ec68d96d3cbcaee170b8c5cfee7f4..bad218f5b115734ea00852a597ea10339d8ddd48 100644
--- a/ui/aura/window_event_dispatcher.cc
+++ b/ui/aura/window_event_dispatcher.cc
@@ -75,7 +75,6 @@ bool IsEventCandidateForHold(const ui::Event& event) {
 
 WindowEventDispatcher::WindowEventDispatcher(WindowTreeHost* host)
     : host_(host),
-      touch_ids_down_(0),
       mouse_pressed_handler_(NULL),
       mouse_moved_handler_(NULL),
       event_dispatch_target_(NULL),
@@ -853,8 +852,8 @@ void WindowEventDispatcher::PreDispatchTouchEvent(Window* target,
                                                   ui::TouchEvent* event) {
   switch (event->type()) {
     case ui::ET_TOUCH_PRESSED:
-      touch_ids_down_ |= (1 << event->touch_id());
-      Env::GetInstance()->set_touch_down(touch_ids_down_ != 0);
+      touch_ids_down_.insert(event->touch_id());
+      Env::GetInstance()->set_touch_down(!touch_ids_down_.empty());
       break;
 
       // Handle ET_TOUCH_CANCELLED only if it has a native event.
@@ -863,9 +862,8 @@ void WindowEventDispatcher::PreDispatchTouchEvent(Window* target,
         break;
       // fallthrough
     case ui::ET_TOUCH_RELEASED:
-      touch_ids_down_ = (touch_ids_down_ | (1 << event->touch_id())) ^
-            (1 << event->touch_id());
-      Env::GetInstance()->set_touch_down(touch_ids_down_ != 0);
+      touch_ids_down_.erase(event->touch_id());
+      Env::GetInstance()->set_touch_down(!touch_ids_down_.empty());
       break;
 
     case ui::ET_TOUCH_MOVED: