Reland: Makes magnifier observe AXEventManager for focus changes

 Bug: 865575

Reland of https://chromium-review.googlesource.com/c/chromium/src/+/1852414

This change differs in:
- only show the viewport widget once all associated state is ready to respond to events. This fixes a potential crash.
- only observe focus events on controls.

Change-Id: I1addbfb4a9d89e738ca6992c3ccd1f88e9546104
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1876688
Commit-Queue: David Tseng <dtseng@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#708721}

ash/magnifier/docked_magnifier_controller_impl.cc

@@ -713,8 +713,6 @@ void DockedMagnifierControllerImpl::CreateMagnifierViewport() {
       GetViewportParentContainerForRoot(current_source_root_window_);
   params.name = kDockedMagnifierViewportWindowName;
   viewport_widget_->Init(std::move(params));
-  viewport_widget_->Show();
-  viewport_widget_->AddObserver(this);
 
   // 2- Create the separator layer right below the viwport widget, parented to
   //    the layer of the root window.
@@ -760,6 +758,11 @@ void DockedMagnifierControllerImpl::CreateMagnifierViewport() {
 
   // 6- Confine the mouse cursor within the remaining part of the display.
   ConfineMouseCursorOutsideViewport();
+
+  // 7- Show the widget, which can trigger events to request movement of the
+  // viewport now that all internal state has been created.
+  viewport_widget_->AddObserver(this);
+  viewport_widget_->Show();
 }
 
 void DockedMagnifierControllerImpl::MaybeCachePointOfInterestMinimumHeight(

chrome/browser/chromeos/accessibility/magnification_manager.cc

@@ -25,6 +25,9 @@
 #include "content/public/browser/notification_source.h"
 #include "content/public/common/service_manager_connection.h"
 #include "services/service_manager/public/cpp/connector.h"
+#include "ui/accessibility/ax_role_properties.h"
+#include "ui/views/accessibility/ax_event_manager.h"
+#include "ui/views/accessibility/view_accessibility.h"
 
 namespace chromeos {
 
@@ -98,6 +101,25 @@ void MagnificationManager::OnProfileWillBeDestroyed(Profile* profile) {
   SetProfile(nullptr);
 }
 
+void MagnificationManager::OnViewEvent(views::View* view,
+                                       ax::mojom::Event event_type) {
+  if (!fullscreen_magnifier_enabled_ && !IsDockedMagnifierEnabled())
+    return;
+
+  if (event_type != ax::mojom::Event::kFocus &&
+      event_type != ax::mojom::Event::kSelection) {
+    return;
+  }
+
+  ui::AXNodeData data;
+  view->GetViewAccessibility().GetAccessibleNodeData(&data);
+
+  // Disallow focus on large containers, which probably should not move the
+  // magnified viewport to the center of the view.
+  if (ui::IsControl(data.role))
+    HandleFocusChanged(view->GetBoundsInScreen(), false);
+}
+
 void MagnificationManager::SetProfileForTest(Profile* profile) {
   SetProfile(profile);
 }
@@ -110,10 +132,12 @@ MagnificationManager::MagnificationManager() {
   registrar_.Add(this, content::NOTIFICATION_FOCUS_CHANGED_IN_PAGE,
                  content::NotificationService::AllSources());
   user_manager::UserManager::Get()->AddSessionStateObserver(this);
+  views::AXEventManager::Get()->AddObserver(this);
 }
 
 MagnificationManager::~MagnificationManager() {
   CHECK(this == g_magnification_manager);
+  views::AXEventManager::Get()->RemoveObserver(this);
   user_manager::UserManager::Get()->RemoveSessionStateObserver(this);
 }
 
@@ -281,17 +305,22 @@ void MagnificationManager::HandleFocusChangedInPage(
   if (node_details->is_editable_node)
     return;
 
-  const gfx::Rect& bounds_in_screen = node_details->node_bounds_in_screen;
+  HandleFocusChanged(node_details->node_bounds_in_screen,
+                     node_details->is_editable_node);
+}
+
+void MagnificationManager::HandleFocusChanged(const gfx::Rect& bounds_in_screen,
+                                              bool is_editable) {
   if (bounds_in_screen.IsEmpty())
     return;
 
   // Fullscreen magnifier and docked magnifier are mutually exclusive.
   if (fullscreen_magnifier_enabled_) {
     ash::Shell::Get()->magnification_controller()->HandleFocusedNodeChanged(
-        node_details->is_editable_node, node_details->node_bounds_in_screen);
+        is_editable, bounds_in_screen);
     return;
   }
-  DCHECK(docked_magnifier_enabled);
+  DCHECK(IsDockedMagnifierEnabled());
   ash::DockedMagnifierController::Get()->CenterOnPoint(
       bounds_in_screen.CenterPoint());
 }

chrome/browser/chromeos/accessibility/magnification_manager.h

@@ -13,6 +13,7 @@
 #include "components/user_manager/user_manager.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
+#include "ui/views/accessibility/ax_event_observer.h"
 
 class PrefChangeRegistrar;
 
@@ -33,7 +34,8 @@ namespace chromeos {
 class MagnificationManager
     : public content::NotificationObserver,
       public user_manager::UserManager::UserSessionStateObserver,
-      public ProfileObserver {
+      public ProfileObserver,
+      public views::AXEventObserver {
  public:
   // Creates an instance of MagnificationManager. This should be called once.
   static void Initialize();
@@ -65,6 +67,9 @@ class MagnificationManager
   // ProfileObserver:
   void OnProfileWillBeDestroyed(Profile* profile) override;
 
+  // views::AXEventObserver:
+  void OnViewEvent(views::View* view, ax::mojom::Event event_type) override;
+
   void SetProfileForTest(Profile* profile);
 
  private:
@@ -91,6 +96,9 @@ class MagnificationManager
   // Called when received content::NOTIFICATION_FOCUS_CHANGED_IN_PAGE.
   void HandleFocusChangedInPage(const content::NotificationDetails& details);
 
+  // Called in response to AXEventObserver.
+  void HandleFocusChanged(const gfx::Rect& bounds_in_screen, bool is_editable);
+
   Profile* profile_ = nullptr;
   ScopedObserver<Profile, ProfileObserver> profile_observer_{this};