Move ViewsDelegate::NotifyAccessibilityEvent to an observer pattern

Introduce AXEventManager to maintain an ObserverList of objects
interested in views accessibility events.

This makes testing easier by eliminating the need for several
TestViewsDelegates.

BUG=908884
TEST=views_unittests, views_mus_unittests, browser_tests

Change-Id: Ic7017444fec7e694675ad675e0fefaf78b622130
Reviewed-on: https://chromium-review.googlesource.com/c/1352265Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612192}

ash/test/ash_test_views_delegate.cc

@@ -5,7 +5,6 @@
 #include "ash/test/ash_test_views_delegate.h"
 
 #include "ash/shell.h"
-#include "ash/test/ash_test_helper.h"
 
 namespace ash {
 
@@ -31,17 +30,6 @@ void AshTestViewsDelegate::OnBeforeWidgetInit(
   TestViewsDelegate::OnBeforeWidgetInit(params, delegate);
 }
 
-void AshTestViewsDelegate::NotifyAccessibilityEvent(
-    views::View* view,
-    ax::mojom::Event event_type) {
-  TestViewsDelegate::NotifyAccessibilityEvent(view, event_type);
-
-  if (test_accessibility_event_delegate_) {
-    test_accessibility_event_delegate_->NotifyAccessibilityEvent(view,
-                                                                 event_type);
-  }
-}
-
 views::TestViewsDelegate::ProcessMenuAcceleratorResult
 AshTestViewsDelegate::ProcessAcceleratorWhileMenuShowing(
     const ui::Accelerator& accelerator) {

ash/test/ash_test_views_delegate.h

@@ -10,14 +10,6 @@
 
 namespace ash {
 
-class TestAccessibilityEventDelegate {
- public:
-  TestAccessibilityEventDelegate() {}
-  virtual ~TestAccessibilityEventDelegate() {}
-  virtual void NotifyAccessibilityEvent(views::View* view,
-                                        ax::mojom::Event event_type) = 0;
-};
-
 // Ash specific ViewsDelegate. In addition to creating a TestWebContents this
 // parents widget with no parent/context to the shell. This is created by
 // default AshTestHelper.
@@ -32,18 +24,10 @@ class AshTestViewsDelegate : public views::TestViewsDelegate {
   // TODO: remove this and ban usage of AshTestHelper outside of ash.
   void set_running_outside_ash() { running_outside_ash_ = true; }
 
-  // Not owned.
-  void set_test_accessibility_event_delegate(
-      TestAccessibilityEventDelegate* test_accessibility_event_delegate) {
-    test_accessibility_event_delegate_ = test_accessibility_event_delegate;
-  }
-
   // Overriden from TestViewsDelegate.
   void OnBeforeWidgetInit(
       views::Widget::InitParams* params,
       views::internal::NativeWidgetDelegate* delegate) override;
-  void NotifyAccessibilityEvent(views::View* view,
-                                ax::mojom::Event event_type) override;
   views::TestViewsDelegate::ProcessMenuAcceleratorResult
   ProcessAcceleratorWhileMenuShowing(
       const ui::Accelerator& accelerator) override;
@@ -57,9 +41,6 @@ class AshTestViewsDelegate : public views::TestViewsDelegate {
   // matches with this.
   ui::Accelerator close_menu_accelerator_;
 
-  // Not owned.
-  TestAccessibilityEventDelegate* test_accessibility_event_delegate_ = nullptr;
-
   bool running_outside_ash_ = false;
 
   DISALLOW_COPY_AND_ASSIGN(AshTestViewsDelegate);

chrome/browser/ui/aura/accessibility/automation_manager_aura.cc

@@ -21,6 +21,7 @@
 #include "ui/aura/window.h"
 #include "ui/aura/window_tree_host.h"
 #include "ui/views/accessibility/ax_aura_obj_wrapper.h"
+#include "ui/views/accessibility/ax_event_manager.h"
 #include "ui/views/view.h"
 #include "ui/views/widget/widget.h"
 
@@ -43,6 +44,8 @@ void AutomationManagerAura::Enable() {
   Reset(false);
 
   SendEvent(current_tree_->GetRoot(), ax::mojom::Event::kLoadComplete);
+  // Intentionally not reset at shutdown since we cannot rely on the shutdown
+  // ordering of two base::Singletons.
   views::AXAuraObjCache::GetInstance()->SetDelegate(this);
 
 #if defined(OS_CHROMEOS)
@@ -70,7 +73,7 @@ void AutomationManagerAura::Disable() {
 #endif
 }
 
-void AutomationManagerAura::HandleEvent(views::View* view,
+void AutomationManagerAura::OnViewEvent(views::View* view,
                                         ax::mojom::Event event_type) {
   CHECK(view);
 
@@ -161,9 +164,12 @@ AutomationManagerAura::AutomationManagerAura()
     : AXHostDelegate(ui::DesktopAXTreeID()),
       enabled_(false),
       processing_events_(false),
-      weak_ptr_factory_(this) {}
+      weak_ptr_factory_(this) {
+  views::AXEventManager::Get()->AddObserver(this);
+}
 
 AutomationManagerAura::~AutomationManagerAura() {
+  views::AXEventManager::Get()->RemoveObserver(this);
 }
 
 void AutomationManagerAura::Reset(bool reset_serializer) {

chrome/browser/ui/aura/accessibility/automation_manager_aura.h

@@ -18,6 +18,7 @@
 #include "ui/accessibility/ax_host_delegate.h"
 #include "ui/accessibility/ax_tree_serializer.h"
 #include "ui/views/accessibility/ax_aura_obj_cache.h"
+#include "ui/views/accessibility/ax_event_observer.h"
 
 namespace base {
 template <typename T>
@@ -36,7 +37,8 @@ struct ExtensionMsg_AccessibilityEventBundleParams;
 
 // Manages a tree of automation nodes.
 class AutomationManagerAura : public ui::AXHostDelegate,
-                              public views::AXAuraObjCache::Delegate {
+                              public views::AXAuraObjCache::Delegate,
+                              public views::AXEventObserver {
  public:
   // Get the single instance of this class.
   static AutomationManagerAura* GetInstance();
@@ -47,9 +49,6 @@ class AutomationManagerAura : public ui::AXHostDelegate,
   // Disable automation support for views.
   void Disable();
 
-  // Handle an event fired upon a |View|.
-  void HandleEvent(views::View* view, ax::mojom::Event event_type);
-
   // Handle an event fired upon the root view.
   void HandleEvent(ax::mojom::Event event_type);
 
@@ -63,6 +62,9 @@ class AutomationManagerAura : public ui::AXHostDelegate,
   void OnEvent(views::AXAuraObjWrapper* aura_obj,
                ax::mojom::Event event_type) override;
 
+  // views::AXEventObserver:
+  void OnViewEvent(views::View* view, ax::mojom::Event event_type) override;
+
   void set_event_bundle_callback_for_testing(
       base::RepeatingCallback<void(ExtensionMsg_AccessibilityEventBundleParams)>
           callback) {

chrome/browser/ui/views/chrome_views_delegate.cc

@@ -20,10 +20,6 @@
 #include "ui/gfx/geometry/rect.h"
 #include "ui/views/widget/widget.h"
 
-#if defined(USE_AURA)
-#include "chrome/browser/ui/aura/accessibility/automation_manager_aura.h"
-#endif
-
 #if defined(OS_CHROMEOS)
 #include "chrome/browser/ui/views/touch_selection_menu_runner_chromeos.h"
 #endif
@@ -136,14 +132,6 @@ bool ChromeViewsDelegate::GetSavedWindowPlacement(
   return true;
 }
 
-void ChromeViewsDelegate::NotifyAccessibilityEvent(
-    views::View* view,
-    ax::mojom::Event event_type) {
-#if defined(USE_AURA)
-  AutomationManagerAura::GetInstance()->HandleEvent(view, event_type);
-#endif
-}
-
 void ChromeViewsDelegate::AddRef() {
   if (ref_count_ == 0u) {
     keep_alive_.reset(

chrome/browser/ui/views/chrome_views_delegate.h

@@ -14,7 +14,6 @@
 #include "base/location.h"
 #include "base/macros.h"
 #include "build/build_config.h"
-#include "ui/accessibility/ax_enums.mojom.h"
 #include "ui/views/views_delegate.h"
 
 class ScopedKeepAlive;
@@ -33,8 +32,6 @@ class ChromeViewsDelegate : public views::ViewsDelegate {
                                const std::string& window_name,
                                gfx::Rect* bounds,
                                ui::WindowShowState* show_state) const override;
-  void NotifyAccessibilityEvent(views::View* view,
-                                ax::mojom::Event event_type) override;
 #if defined(OS_CHROMEOS)
   ProcessMenuAcceleratorResult ProcessAcceleratorWhileMenuShowing(
       const ui::Accelerator& accelerator) override;

chrome/browser/ui/views/tabs/tab_strip_unittest.cc

@@ -17,7 +17,6 @@
 #include "chrome/browser/ui/views/tabs/tab_strip_observer.h"
 #include "chrome/browser/ui/views/tabs/tab_style.h"
 #include "chrome/test/base/testing_profile.h"
-#include "chrome/test/views/chrome_test_views_delegate.h"
 #include "chrome/test/views/chrome_views_test_base.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/base/material_design/material_design_controller.h"
@@ -27,6 +26,8 @@
 #include "ui/gfx/geometry/rect_conversions.h"
 #include "ui/gfx/path.h"
 #include "ui/gfx/skia_util.h"
+#include "ui/views/accessibility/ax_event_manager.h"
+#include "ui/views/accessibility/ax_event_observer.h"
 #include "ui/views/controls/label.h"
 #include "ui/views/view.h"
 #include "ui/views/view_targeter.h"
@@ -44,12 +45,16 @@ views::View* FindTabView(views::View* view) {
   return current;
 }
 
-class TabStripTestViewsDelegate : public ChromeTestViewsDelegate {
+class TestAXEventObserver : public views::AXEventObserver {
  public:
-  TabStripTestViewsDelegate() = default;
-  ~TabStripTestViewsDelegate() override = default;
-  void NotifyAccessibilityEvent(views::View* view,
-                                ax::mojom::Event event_type) override {
+  TestAXEventObserver() { views::AXEventManager::Get()->AddObserver(this); }
+
+  ~TestAXEventObserver() override {
+    views::AXEventManager::Get()->RemoveObserver(this);
+  }
+
+  // views::AXEventObserver:
+  void OnViewEvent(views::View* view, ax::mojom::Event event_type) override {
     if (event_type == ax::mojom::Event::kSelectionRemove) {
       remove_count_++;
     }
@@ -64,7 +69,8 @@ class TabStripTestViewsDelegate : public ChromeTestViewsDelegate {
  private:
   int add_count_ = 0;
   int remove_count_ = 0;
-  DISALLOW_COPY_AND_ASSIGN(TabStripTestViewsDelegate);
+
+  DISALLOW_COPY_AND_ASSIGN(TestAXEventObserver);
 };
 
 class AnimationWaiter {
@@ -170,13 +176,6 @@ class TabStripTest : public ChromeViewsTestBase,
   }
 
  protected:
-  std::unique_ptr<views::TestViewsDelegate> CreateTestViewsDelegate() override {
-    std::unique_ptr<TabStripTestViewsDelegate> delegate =
-        std::make_unique<TabStripTestViewsDelegate>();
-    test_views_delegate_ = delegate.get();
-    return delegate;
-  }
-
   bool IsShowingAttentionIndicator(Tab* tab) {
     return tab->icon_->ShowingAttentionIndicator();
   }
@@ -222,7 +221,6 @@ class TabStripTest : public ChromeViewsTestBase,
   // Owns |tab_strip_|.
   views::View parent_;
   TabStrip* tab_strip_ = nullptr;
-  TabStripTestViewsDelegate* test_views_delegate_ = nullptr;
   std::unique_ptr<views::Widget> widget_;
 
  private:
@@ -236,6 +234,8 @@ TEST_P(TabStripTest, GetModelCount) {
 }
 
 TEST_P(TabStripTest, AccessibilityEvents) {
+  TestAXEventObserver observer;
+
   // When adding tabs, SetSelection() is called after AddTabAt(), as
   // otherwise the index would not be meaningful.
   tab_strip_->AddTabAt(0, TabRendererData(), false);
@@ -243,16 +243,16 @@ TEST_P(TabStripTest, AccessibilityEvents) {
   ui::ListSelectionModel selection;
   selection.SetSelectedIndex(1);
   tab_strip_->SetSelection(selection);
-  EXPECT_EQ(1, test_views_delegate_->add_count());
-  EXPECT_EQ(0, test_views_delegate_->remove_count());
+  EXPECT_EQ(1, observer.add_count());
+  EXPECT_EQ(0, observer.remove_count());
 
   // When removing tabs, SetSelection() is called before RemoveTabAt(), as
   // otherwise the index would not be meaningful.
   selection.SetSelectedIndex(0);
   tab_strip_->SetSelection(selection);
   tab_strip_->RemoveTabAt(nullptr, 1, true);
-  EXPECT_EQ(2, test_views_delegate_->add_count());
-  EXPECT_EQ(1, test_views_delegate_->remove_count());
+  EXPECT_EQ(2, observer.add_count());
+  EXPECT_EQ(1, observer.remove_count());
 }
 
 TEST_P(TabStripTest, IsValidModelIndex) {

chrome/test/views/chrome_views_test_base.cc

@@ -11,11 +11,6 @@ ChromeViewsTestBase::ChromeViewsTestBase() {}
 ChromeViewsTestBase::~ChromeViewsTestBase() {}
 
 void ChromeViewsTestBase::SetUp() {
-  set_views_delegate(CreateTestViewsDelegate());
+  set_views_delegate(std::make_unique<ChromeTestViewsDelegate>());
   views::ViewsTestBase::SetUp();
 }
-
-std::unique_ptr<views::TestViewsDelegate>
-ChromeViewsTestBase::CreateTestViewsDelegate() {
-  return std::make_unique<ChromeTestViewsDelegate>();
-}

chrome/test/views/chrome_views_test_base.h

@@ -20,9 +20,6 @@ class ChromeViewsTestBase : public views::ViewsTestBase {
   // views::ViewsTestBase:
   void SetUp() override;
 
-  // Subclasses can override to provide their own TestViewsDelegate
-  virtual std::unique_ptr<views::TestViewsDelegate> CreateTestViewsDelegate();
-
  private:
   DISALLOW_COPY_AND_ASSIGN(ChromeViewsTestBase);
 };

ui/views/BUILD.gn

@@ -59,6 +59,8 @@ jumbo_component("views") {
     "../views_bridge_mac/bridged_native_widget_impl.h",
     "../views_bridge_mac/native_widget_mac_nswindow.h",
     "../views_bridge_mac/window_touch_bar_delegate.h",
+    "accessibility/ax_event_manager.h",
+    "accessibility/ax_event_observer.h",
     "accessibility/ax_virtual_view.h",
     "accessibility/view_accessibility.h",
     "accessibility/view_accessibility_utils.h",
@@ -266,6 +268,8 @@ jumbo_component("views") {
     # TODO(ccameron): Move these sources to the views_bridge_mac component
     "../views_bridge_mac/bridged_native_widget_impl.mm",
     "../views_bridge_mac/native_widget_mac_nswindow.mm",
+    "accessibility/ax_event_manager.cc",
+    "accessibility/ax_event_observer.cc",
     "accessibility/ax_virtual_view.cc",
     "accessibility/view_accessibility.cc",
     "accessibility/view_accessibility_utils.cc",

ui/views/accessibility/ax_event_manager.cc

+// Copyright 2018 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/views/accessibility/ax_event_manager.h"
+
+#include "base/no_destructor.h"
+#include "ui/views/accessibility/ax_event_observer.h"
+
+namespace views {
+
+AXEventManager::AXEventManager() = default;
+
+AXEventManager::~AXEventManager() = default;
+
+// static
+AXEventManager* AXEventManager::Get() {
+  static base::NoDestructor<AXEventManager> instance;
+  return instance.get();
+}
+
+void AXEventManager::AddObserver(AXEventObserver* observer) {
+  observers_.AddObserver(observer);
+}
+
+void AXEventManager::RemoveObserver(AXEventObserver* observer) {
+  observers_.RemoveObserver(observer);
+}
+
+void AXEventManager::NotifyViewEvent(views::View* view,
+                                     ax::mojom::Event event_type) {
+  for (AXEventObserver& observer : observers_)
+    observer.OnViewEvent(view, event_type);
+}
+
+}  // namespace views

ui/views/accessibility/ax_event_manager.h

+// Copyright 2018 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.
+
+#ifndef UI_VIEWS_ACCESSIBILITY_AX_EVENT_MANAGER_H_
+#define UI_VIEWS_ACCESSIBILITY_AX_EVENT_MANAGER_H_
+
+#include "base/macros.h"
+#include "base/observer_list.h"
+#include "ui/accessibility/ax_enums.mojom.h"
+#include "ui/views/views_export.h"
+
+namespace views {
+
+class AXEventObserver;
+class View;
+
+// AXEventManager allows observation of accessibility events for all views.
+class VIEWS_EXPORT AXEventManager {
+ public:
+  AXEventManager();
+  ~AXEventManager();
+
+  // Returns the singleton instance.
+  static AXEventManager* Get();
+
+  void AddObserver(AXEventObserver* observer);
+  void RemoveObserver(AXEventObserver* observer);
+
+  // Notifies observers of an accessibility event. |view| must not be null.
+  void NotifyViewEvent(views::View* view, ax::mojom::Event event_type);
+
+ private:
+  base::ObserverList<AXEventObserver> observers_;
+
+  DISALLOW_COPY_AND_ASSIGN(AXEventManager);
+};
+
+}  // namespace views
+
+#endif  // UI_VIEWS_ACCESSIBILITY_AX_EVENT_MANAGER_H_

ui/views/accessibility/ax_event_observer.cc

+// Copyright 2018 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/views/accessibility/ax_event_observer.h"
+
+namespace views {
+
+AXEventObserver::AXEventObserver() = default;
+
+AXEventObserver::~AXEventObserver() = default;
+
+}  // namespace views

ui/views/accessibility/ax_event_observer.h

+// Copyright 2018 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.
+
+#ifndef UI_VIEWS_ACCESSIBILITY_AX_EVENT_OBSERVER_H_
+#define UI_VIEWS_ACCESSIBILITY_AX_EVENT_OBSERVER_H_
+
+#include "base/observer_list_types.h"
+#include "ui/accessibility/ax_enums.mojom.h"
+#include "ui/views/views_export.h"
+
+namespace views {
+
+class View;
+
+// AXEventObserver is notified for accessibility events on all views.
+class VIEWS_EXPORT AXEventObserver : public base::CheckedObserver {
+ public:
+  virtual void OnViewEvent(views::View* view, ax::mojom::Event event_type) = 0;
+
+ protected:
+  AXEventObserver();
+  ~AXEventObserver() override;
+};
+
+}  // namespace views
+
+#endif  // UI_VIEWS_ACCESSIBILITY_AX_EVENT_OBSERVER_H_

ui/views/accessibility/view_ax_platform_node_delegate_unittest.cc

@@ -13,6 +13,8 @@
 #include "ui/gfx/geometry/size.h"
 #include "ui/views/accessibility/ax_aura_obj_cache.h"
 #include "ui/views/accessibility/ax_aura_obj_wrapper.h"
+#include "ui/views/accessibility/ax_event_manager.h"
+#include "ui/views/accessibility/ax_event_observer.h"
 #include "ui/views/accessibility/ax_widget_obj_wrapper.h"
 #include "ui/views/controls/button/button.h"
 #include "ui/views/controls/label.h"
@@ -178,13 +180,16 @@ class DerivedTestView : public View {
   void OnBlur() override { SetVisible(false); }
 };
 
-class AxTestViewsDelegate : public TestViewsDelegate {
+class TestAXEventObserver : public AXEventObserver {
  public:
-  AxTestViewsDelegate() = default;
-  ~AxTestViewsDelegate() override = default;
+  TestAXEventObserver() { AXEventManager::Get()->AddObserver(this); }
 
-  void NotifyAccessibilityEvent(View* view,
-                                ax::mojom::Event event_type) override {
+  ~TestAXEventObserver() override {
+    AXEventManager::Get()->RemoveObserver(this);
+  }
+
+  // AXEventObserver:
+  void OnViewEvent(View* view, ax::mojom::Event event_type) override {
     AXAuraObjCache* ax = AXAuraObjCache::GetInstance();
     std::vector<AXAuraObjWrapper*> out_children;
     AXAuraObjWrapper* ax_obj = ax->GetOrCreate(view->GetWidget());
@@ -192,24 +197,17 @@ class AxTestViewsDelegate : public TestViewsDelegate {
   }
 
  private:
-  DISALLOW_COPY_AND_ASSIGN(AxTestViewsDelegate);
+  DISALLOW_COPY_AND_ASSIGN(TestAXEventObserver);
 };
 
-class ViewAccessibilityTest : public ViewsTestBase {
- public:
-  ViewAccessibilityTest() = default;
-  ~ViewAccessibilityTest() override = default;
-  void SetUp() override {
-    std::unique_ptr<TestViewsDelegate> views_delegate(
-        new AxTestViewsDelegate());
-    set_views_delegate(std::move(views_delegate));
-    ViewsTestBase::SetUp();
-  }
-};
+using ViewAccessibilityTest = ViewsTestBase;
 
 // Check if the destruction of the widget ends successfully if |view|'s
 // visibility changed during destruction.
 TEST_F(ViewAccessibilityTest, LayoutCalledInvalidateRootView) {
+  // TODO: Construct a real AutomationManagerAura rather than using this
+  // observer to simulate it.
+  TestAXEventObserver observer;
   std::unique_ptr<Widget> widget(new Widget);
   Widget::InitParams params = CreateParams(Widget::InitParams::TYPE_POPUP);
   params.ownership = Widget::InitParams::WIDGET_OWNS_NATIVE_WIDGET;

ui/views/controls/slider_unittest.cc

@@ -18,8 +18,9 @@
 #include "ui/events/gesture_event_details.h"
 #include "ui/events/keycodes/keyboard_codes.h"
 #include "ui/events/test/event_generator.h"
+#include "ui/views/accessibility/ax_event_manager.h"
+#include "ui/views/accessibility/ax_event_observer.h"
 #include "ui/views/test/slider_test_api.h"
-#include "ui/views/test/test_views_delegate.h"
 #include "ui/views/test/views_test_base.h"
 #include "ui/views/view.h"
 #include "ui/views/widget/widget.h"
@@ -118,29 +119,37 @@ void TestSliderListener::SliderDragEnded(views::Slider* sender) {
   last_drag_ended_epoch_ = ++last_event_epoch_;
 }
 
-}  // namespace
+class TestAXEventObserver : public views::AXEventObserver {
+ public:
+  TestAXEventObserver() { views::AXEventManager::Get()->AddObserver(this); }
 
-namespace views {
+  ~TestAXEventObserver() override {
+    views::AXEventManager::Get()->RemoveObserver(this);
+  }
 
-// Base test fixture for Slider tests.
-class SliderTest : public views::ViewsTestBase {
- public:
-  class SliderTestViewsDelegate : public views::TestViewsDelegate {
-   public:
-    bool has_value_changed() { return has_value_changed_; }
+  bool value_changed() const { return value_changed_; }
 
-   private:
-    void NotifyAccessibilityEvent(View* view,
-                                  ax::mojom::Event event_type) override {
+  // views::AXEventObserver:
+  void OnViewEvent(views::View* view, ax::mojom::Event event_type) override {
     if (event_type == ax::mojom::Event::kValueChanged)
-        has_value_changed_ = true;
+      value_changed_ = true;
   }
 
-    bool has_value_changed_ = false;
-  };
+ private:
+  bool value_changed_ = false;
+
+  DISALLOW_COPY_AND_ASSIGN(TestAXEventObserver);
+};
+
+}  // namespace
+
+namespace views {
 
-  SliderTest();
-  ~SliderTest() override;
+// Base test fixture for Slider tests.
+class SliderTest : public views::ViewsTestBase {
+ public:
+  SliderTest() = default;
+  ~SliderTest() override = default;
 
  protected:
   Slider* slider() {
@@ -169,43 +178,26 @@ class SliderTest : public views::ViewsTestBase {
     return event_generator_.get();
   }
 
-  SliderTestViewsDelegate* delegate() { return delegate_; }
-
  private:
   // The Slider to be tested.
-  Slider* slider_;
+  Slider* slider_ = nullptr;
   // A simple SliderListener test double.
   TestSliderListener slider_listener_;
   // Stores the default locale at test setup so it can be restored
   // during test teardown.
   std::string default_locale_;
   // The maximum x value within the bounds of the slider.
-  int max_x_;
+  int max_x_ = 0;
   // The maximum y value within the bounds of the slider.
-  int max_y_;
+  int max_y_ = 0;
   // The widget container for the slider being tested.
-  views::Widget* widget_;
+  views::Widget* widget_ = nullptr;
   // An event generator.
   std::unique_ptr<ui::test::EventGenerator> event_generator_;
-  // A TestViewsDelegate that intercepts accessibility notifications. Weak.
-  SliderTestViewsDelegate* delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(SliderTest);
 };
 
-SliderTest::SliderTest()
-    : slider_(NULL),
-      default_locale_(),
-      max_x_(0),
-      max_y_(0),
-      delegate_(new SliderTestViewsDelegate()) {
-  std::unique_ptr<views::TestViewsDelegate> delegate(delegate_);
-  set_views_delegate(std::move(delegate));
-}
-
-SliderTest::~SliderTest() {
-}
-
 void SliderTest::SetUp() {
   views::ViewsTestBase::SetUp();
 
@@ -401,7 +393,8 @@ TEST_F(SliderTest, SliderListenerEventsForMultiFingerScrollGesture) {
 // Verifies the correct SliderListener events are raised for an accessible
 // slider.
 TEST_F(SliderTest, SliderRaisesA11yEvents) {
-  EXPECT_FALSE(delegate()->has_value_changed());
+  TestAXEventObserver observer;
+  EXPECT_FALSE(observer.value_changed());
 
   // First, detach/reattach the slider without setting value.
   // Temporarily detach the slider.
@@ -410,18 +403,18 @@ TEST_F(SliderTest, SliderRaisesA11yEvents) {
 
   // Re-attachment should cause nothing to get fired.
   root_view->AddChildView(slider());
-  EXPECT_FALSE(delegate()->has_value_changed());
+  EXPECT_FALSE(observer.value_changed());
 
   // Now, set value before reattaching.
   root_view->RemoveChildView(slider());
 
   // Value changes won't trigger accessibility events before re-attachment.
   slider()->SetValue(22);
-  EXPECT_FALSE(delegate()->has_value_changed());
+  EXPECT_FALSE(observer.value_changed());
 
   // Re-attachment should trigger the value change.
   root_view->AddChildView(slider());
-  EXPECT_TRUE(delegate()->has_value_changed());
+  EXPECT_TRUE(observer.value_changed());
 }
 
 #endif  // !defined(OS_MACOSX) || defined(USE_AURA)

ui/views/mus/ax_remote_host.cc

@@ -18,6 +18,7 @@
 #include "ui/display/display.h"
 #include "ui/display/screen.h"
 #include "ui/views/accessibility/ax_aura_obj_wrapper.h"
+#include "ui/views/accessibility/ax_event_manager.h"
 #include "ui/views/mus/ax_tree_source_mus.h"
 #include "ui/views/mus/mus_client.h"
 #include "ui/views/view.h"
@@ -30,6 +31,7 @@ using display::Screen;
 namespace views {
 
 AXRemoteHost::AXRemoteHost() {
+  AXEventManager::Get()->AddObserver(this);
   AXAuraObjCache::GetInstance()->SetDelegate(this);
 }
 
@@ -37,6 +39,7 @@ AXRemoteHost::~AXRemoteHost() {
   if (widget_)
     StopMonitoringWidget();
   AXAuraObjCache::GetInstance()->SetDelegate(nullptr);
+  AXEventManager::Get()->RemoveObserver(this);
 }
 
 void AXRemoteHost::Init(service_manager::Connector* connector) {
@@ -98,19 +101,6 @@ void AXRemoteHost::StopMonitoringWidget() {
   tree_source_.reset();
 }
 
-void AXRemoteHost::HandleEvent(View* view, ax::mojom::Event event_type) {
-  CHECK(view);
-
-  if (!enabled_)
-    return;
-
-  // Can return null for views without a widget.
-  AXAuraObjWrapper* aura_obj = AXAuraObjCache::GetInstance()->GetOrCreate(view);
-  if (!aura_obj)
-    return;
-  SendEvent(aura_obj, event_type);
-}
-
 void AXRemoteHost::OnAutomationEnabled(bool enabled) {
   if (enabled)
     Enable();
@@ -170,6 +160,19 @@ void AXRemoteHost::OnEvent(AXAuraObjWrapper* aura_obj,
   SendEvent(aura_obj, event_type);
 }
 
+void AXRemoteHost::OnViewEvent(View* view, ax::mojom::Event event_type) {
+  CHECK(view);
+
+  if (!enabled_)
+    return;
+
+  // Can return null for views without a widget.
+  AXAuraObjWrapper* aura_obj = AXAuraObjCache::GetInstance()->GetOrCreate(view);
+  if (!aura_obj)
+    return;
+  SendEvent(aura_obj, event_type);
+}
+
 void AXRemoteHost::FlushForTesting() {
   ax_host_ptr_.FlushForTesting();
 }

ui/views/mus/ax_remote_host.h

@@ -15,6 +15,7 @@
 #include "ui/accessibility/mojom/ax_host.mojom.h"
 #include "ui/display/display_observer.h"
 #include "ui/views/accessibility/ax_aura_obj_cache.h"
+#include "ui/views/accessibility/ax_event_observer.h"
 #include "ui/views/mus/mus_export.h"
 #include "ui/views/widget/widget_observer.h"
 
@@ -40,7 +41,8 @@ class Widget;
 class VIEWS_MUS_EXPORT AXRemoteHost : public ax::mojom::AXRemoteHost,
                                       public WidgetObserver,
                                       public display::DisplayObserver,
-                                      public AXAuraObjCache::Delegate {
+                                      public AXAuraObjCache::Delegate,
+                                      public AXEventObserver {
  public:
   AXRemoteHost();
   ~AXRemoteHost() override;
@@ -56,9 +58,6 @@ class VIEWS_MUS_EXPORT AXRemoteHost : public ax::mojom::AXRemoteHost,
   void StartMonitoringWidget(Widget* widget);
   void StopMonitoringWidget();
 
-  // Handles an event fired upon a |view|.
-  void HandleEvent(View* view, ax::mojom::Event event_type);
-
   // ax::mojom::AXRemoteHost:
   void OnAutomationEnabled(bool enabled) override;
   void PerformAction(const ui::AXActionData& action) override;
@@ -76,6 +75,9 @@ class VIEWS_MUS_EXPORT AXRemoteHost : public ax::mojom::AXRemoteHost,
   void OnEvent(AXAuraObjWrapper* aura_obj,
                ax::mojom::Event event_type) override;
 
+  // AXEventObserver:
+  void OnViewEvent(View* view, ax::mojom::Event event_type) override;
+
   void FlushForTesting();
   Widget* widget_for_testing() { return widget_; }
 

ui/views/mus/ax_remote_host_unittest.cc

@@ -117,8 +117,9 @@ AXRemoteHost* CreateRemote(TestAXHostService* service) {
   remote->InitForTesting(service->CreateInterfacePtr());
   remote->FlushForTesting();
   // Install the AXRemoteHost on MusClient so it monitors Widget creation.
+  AXRemoteHost* remote_raw = remote.get();
   MusClientTestApi::SetAXRemoteHost(std::move(remote));
-  return MusClient::Get()->ax_remote_host();
+  return remote_raw;
 }
 
 std::unique_ptr<Widget> CreateTestWidget() {
@@ -193,7 +194,7 @@ TEST_F(AXRemoteHostTest, SendEventOnViewWithNoWidget) {
 
   // Create a view that is not yet associated with the widget.
   views::View view;
-  remote->HandleEvent(&view, ax::mojom::Event::kLocationChanged);
+  remote->OnViewEvent(&view, ax::mojom::Event::kLocationChanged);
   // No crash.
 }
 

ui/views/mus/mus_client.h

@@ -115,8 +115,6 @@ class VIEWS_MUS_EXPORT MusClient : public aura::WindowTreeClientDelegate,
 
   aura::WindowTreeClient* window_tree_client() { return window_tree_client_; }
 
-  AXRemoteHost* ax_remote_host() { return ax_remote_host_.get(); }
-
   // Creates DesktopNativeWidgetAura with DesktopWindowTreeHostMus. This is
   // set as the factory function used for creating NativeWidgets when a
   //  NativeWidget has not been explicitly set.

ui/views/mus/mus_views_delegate.cc

@@ -4,7 +4,6 @@
 
 #include "ui/views/mus/mus_views_delegate.h"
 
-#include "ui/views/mus/ax_remote_host.h"
 #include "ui/views/mus/mus_client.h"
 
 namespace views {
@@ -13,10 +12,4 @@ MusViewsDelegate::MusViewsDelegate() = default;
 
 MusViewsDelegate::~MusViewsDelegate() = default;
 
-void MusViewsDelegate::NotifyAccessibilityEvent(View* view,
-                                                ax::mojom::Event event_type) {
-  if (MusClient::Get()->ax_remote_host())
-    MusClient::Get()->ax_remote_host()->HandleEvent(view, event_type);
-}
-
 }  // namespace views

ui/views/mus/mus_views_delegate.h

@@ -12,15 +12,12 @@
 
 namespace views {
 
+// TODO(jamescook): Move the LayoutProvider and delete this class.
 class VIEWS_MUS_EXPORT MusViewsDelegate : public ViewsDelegate {
  public:
   MusViewsDelegate();
   ~MusViewsDelegate() override;
 
-  // ViewsDelegate:
-  void NotifyAccessibilityEvent(View* view,
-                                ax::mojom::Event event_type) override;
-
  private:
   LayoutProvider layout_provider_;
 

ui/views/view.cc

@@ -44,6 +44,7 @@
 #include "ui/gfx/skia_util.h"
 #include "ui/gfx/transform.h"
 #include "ui/native_theme/native_theme.h"
+#include "ui/views/accessibility/ax_event_manager.h"
 #include "ui/views/accessibility/view_accessibility.h"
 #include "ui/views/background.h"
 #include "ui/views/border.h"
@@ -52,7 +53,6 @@
 #include "ui/views/layout/layout_manager.h"
 #include "ui/views/view_observer.h"
 #include "ui/views/view_tracker.h"
-#include "ui/views/views_delegate.h"
 #include "ui/views/views_switches.h"
 #include "ui/views/widget/native_widget_private.h"
 #include "ui/views/widget/root_view.h"
@@ -1451,8 +1451,7 @@ gfx::NativeViewAccessible View::GetNativeViewAccessible() {
 
 void View::NotifyAccessibilityEvent(ax::mojom::Event event_type,
                                     bool send_native_event) {
-  if (ViewsDelegate::GetInstance())
-    ViewsDelegate::GetInstance()->NotifyAccessibilityEvent(this, event_type);
+  AXEventManager::Get()->NotifyViewEvent(this, event_type);
 
   if (send_native_event && GetWidget())
     GetViewAccessibility().NotifyAccessibilityEvent(event_type);

ui/views/views_delegate.cc

@@ -61,9 +61,6 @@ bool ViewsDelegate::GetSavedWindowPlacement(
   return false;
 }
 
-void ViewsDelegate::NotifyAccessibilityEvent(View* view,
-                                             ax::mojom::Event event_type) {}
-
 void ViewsDelegate::NotifyMenuItemFocused(const base::string16& menu_name,
                                           const base::string16& menu_item_name,
                                           int item_index,

ui/views/views_delegate.h

@@ -17,7 +17,6 @@
 #include "base/macros.h"
 #include "base/strings/string16.h"
 #include "build/build_config.h"
-#include "ui/accessibility/ax_enums.mojom.h"
 #include "ui/base/ui_base_types.h"
 #include "ui/gfx/native_widget_types.h"
 #include "ui/views/views_export.h"
@@ -37,7 +36,6 @@ namespace views {
 
 class NativeWidget;
 class NonClientFrameView;
-class View;
 class Widget;
 
 #if defined(USE_AURA)
@@ -125,10 +123,6 @@ class VIEWS_EXPORT ViewsDelegate {
                                        gfx::Rect* bounds,
                                        ui::WindowShowState* show_state) const;
 
-  // Handles an event on a |view|. The |view| must not be null.
-  virtual void NotifyAccessibilityEvent(View* view,
-                                        ax::mojom::Event event_type);
-
   // For accessibility, notify the delegate that a menu item was focused
   // so that alternate feedback (speech / magnified text) can be provided.
   virtual void NotifyMenuItemFocused(const base::string16& menu_name,