Refactor TopmostWindowObserver to be EventObserver

It has been an window observer + pre-target event handler to
conduct the watching of topmost windows. During debugging of
a test of tab-dragging, I've noticed that this can't deal with
the destruction of the root window itself.

Actually, it doesn't have to be a pre-target event handler
anymore since there's EventObserver now.

BUG=890071
TEST=existing ash_unittests / services_unittests pass

Change-Id: Ic6750700e73fd3694be5aa00f080f3019e4fbd95
Reviewed-on: https://chromium-review.googlesource.com/c/1303034
Commit-Queue: Jun Mukai <mukai@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603286}

services/ws/topmost_window_observer.cc

@@ -16,17 +16,6 @@
 #include "ui/gfx/geometry/point_f.h"
 #include "ui/wm/core/coordinate_conversion.h"
 
-namespace {
-
-gfx::Point GetLocationInScreen(const ui::LocatedEvent& event) {
-  gfx::Point location_in_screen = event.location();
-  ::wm::ConvertPointToScreen(static_cast<aura::Window*>(event.target()),
-                             &location_in_screen);
-  return location_in_screen;
-}
-
-}  // namespace
-
 namespace ws {
 
 TopmostWindowObserver::TopmostWindowObserver(WindowTree* window_tree,
@@ -35,50 +24,37 @@ TopmostWindowObserver::TopmostWindowObserver(WindowTree* window_tree,
     : window_tree_(window_tree),
       source_(source),
       last_target_(initial_target),
-      root_(initial_target->GetRootWindow()) {
-  root_->AddPreTargetHandler(this, ui::EventTarget::Priority::kSystem);
+      env_(initial_target->env()) {
+  std::set<ui::EventType> types;
   if (source == mojom::MoveLoopSource::MOUSE) {
-    last_location_ =
-        root_->GetHost()->dispatcher()->GetLastMouseLocationInRoot();
-    ::wm::ConvertPointToScreen(root_, &last_location_);
+    types.insert(ui::ET_MOUSE_MOVED);
+    types.insert(ui::ET_MOUSE_DRAGGED);
+    last_location_ = env_->last_mouse_location();
   } else {
+    types.insert(ui::ET_TOUCH_MOVED);
     gfx::PointF point;
-    ui::GestureRecognizer* gesture_recognizer =
-        initial_target->env()->gesture_recognizer();
+    ui::GestureRecognizer* gesture_recognizer = env_->gesture_recognizer();
     if (gesture_recognizer->GetLastTouchPointForTarget(last_target_, &point))
       last_location_ = gfx::Point(point.x(), point.y());
     ::wm::ConvertPointToScreen(last_target_, &last_location_);
   }
+  env_->AddEventObserver(this, env_, types);
   UpdateTopmostWindows();
 }
 
 TopmostWindowObserver::~TopmostWindowObserver() {
-  root_->RemovePreTargetHandler(this);
+  env_->RemoveEventObserver(this);
   if (topmost_)
     topmost_->RemoveObserver(this);
   if (real_topmost_ && topmost_ != real_topmost_)
     real_topmost_->RemoveObserver(this);
 }
 
-void TopmostWindowObserver::OnMouseEvent(ui::MouseEvent* event) {
-  CHECK_EQ(ui::EP_PRETARGET, event->phase());
-  if (source_ != mojom::MoveLoopSource::MOUSE)
-    return;
-  // The event target can change when the dragged browser tab is detached into a
-  // new window.
-  last_target_ = static_cast<aura::Window*>(event->target());
-  last_location_ = GetLocationInScreen(*event);
-  UpdateTopmostWindows();
-}
-
-void TopmostWindowObserver::OnTouchEvent(ui::TouchEvent* event) {
-  CHECK_EQ(ui::EP_PRETARGET, event->phase());
-  if (source_ != mojom::MoveLoopSource::TOUCH)
-    return;
-  // The event target can change when the dragged browser tab is detached into a
-  // new window.
-  last_target_ = static_cast<aura::Window*>(event->target());
-  last_location_ = GetLocationInScreen(*event);
+void TopmostWindowObserver::OnEvent(const ui::Event& event) {
+  CHECK(event.IsLocatedEvent());
+  last_target_ = static_cast<aura::Window*>(event.target());
+  last_location_ = event.AsLocatedEvent()->location();
+  ::wm::ConvertPointToScreen(last_target_, &last_location_);
   UpdateTopmostWindows();
 }
 

services/ws/topmost_window_observer.h

@@ -7,10 +7,11 @@
 
 #include "services/ws/public/mojom/window_tree.mojom.h"
 #include "ui/aura/window_observer.h"
-#include "ui/events/event_handler.h"
+#include "ui/events/event_observer.h"
 #include "ui/gfx/geometry/point.h"
 
 namespace aura {
+class Env;
 class Window;
 }
 
@@ -23,7 +24,7 @@ class WindowTree;
 
 // TODO(mukai): support multiple displays.
 class COMPONENT_EXPORT(WINDOW_SERVICE) TopmostWindowObserver
-    : public ui::EventHandler,
+    : public ui::EventObserver,
       public aura::WindowObserver {
  public:
   // |source| determines the type of the event, and |initial_target| is the
@@ -37,9 +38,8 @@ class COMPONENT_EXPORT(WINDOW_SERVICE) TopmostWindowObserver
  private:
   friend class TopmostWindowObserverTest;
 
-  // ui::EventHandler:
-  void OnMouseEvent(ui::MouseEvent* event) override;
-  void OnTouchEvent(ui::TouchEvent* event) override;
+  // ui::EventObserver:
+  void OnEvent(const ui::Event& event) override;
 
   // aura::WindowObserver:
   void OnWindowVisibilityChanged(aura::Window* window, bool visible) override;
@@ -72,8 +72,7 @@ class COMPONENT_EXPORT(WINDOW_SERVICE) TopmostWindowObserver
   // The topmost window (including |last_target_|) under the cursor/touch.
   aura::Window* real_topmost_ = nullptr;
 
-  // The attached root window.
-  aura::Window* root_;
+  aura::Env* env_;
 
   DISALLOW_COPY_AND_ASSIGN(TopmostWindowObserver);
 };