mash: make Env::last_mouse_location() accurate for Mus

ui/aura/mus/mus_mouse_location_updater.cc

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ui/aura/mus/mus_mouse_location_updater.h"
+
+#include "ui/aura/env.h"
+#include "ui/events/event.h"
+
+namespace aura {
+namespace {
+
+bool IsMouseEventWithLocation(const ui::Event& event) {
+  // All mouse events except exited, capture, and wheel which mus doesn't
+  // include locations for.
+  switch (event.type()) {
+    case ui::ET_MOUSE_PRESSED:
+    case ui::ET_MOUSE_DRAGGED:
+    case ui::ET_MOUSE_RELEASED:
+    case ui::ET_MOUSE_MOVED:
+    case ui::ET_MOUSE_ENTERED:
+      return true;
+    default:
+      break;
+  }
+  return false;
+}
+
+}  // namespace
+
+MusMouseLocationUpdater::MusMouseLocationUpdater() {}
+
+MusMouseLocationUpdater::~MusMouseLocationUpdater() {
+  // Should never be destroyed while in the middle of processing an event.
+  DCHECK(!observing_message_loop_);
+}
+
+void MusMouseLocationUpdater::OnEventProcessingStarted(const ui::Event& event) {
+  // Should never process an event while processing another event, unless
+  // a nested message loop is spun, which sets |observing_message_loop_| to
+  // false.
+  DCHECK(!observing_message_loop_);
+
+  if (!IsMouseEventWithLocation(event))
+    return;
+
+  Env::GetInstance()->set_last_mouse_location(
+      event.AsMouseEvent()->root_location());
+  Env::GetInstance()->get_last_mouse_location_from_mus_ = false;

[sadrul, 2017/01/27 21:08:36]

Maybe call this |last_mouse_location_is_valid_| (and set to true from here)?
That I think would make the code in Env read a little easier.

+  observing_message_loop_ = true;
+  base::MessageLoop::current()->AddNestingObserver(this);

[sadrul, 2017/01/27 21:08:36]

Is it better to just leave it always added as a nesting observer instead of
add/removing for each event?

+}
+
+void MusMouseLocationUpdater::OnEventProcessingFinished() {
+  if (!observing_message_loop_)
+    return;
+
+  StopObserving();
+}
+
+void MusMouseLocationUpdater::StopObserving() {
+  DCHECK(observing_message_loop_);
+  observing_message_loop_ = false;
+  base::MessageLoop::current()->RemoveNestingObserver(this);
+  Env::GetInstance()->get_last_mouse_location_from_mus_ = true;
+}
+
+void MusMouseLocationUpdater::OnBeginNestedMessageLoop() {
+  StopObserving();
+}
+
+}  // namespace aura