AutomationManagerAura::HandleEvent sends events on the root object by default

Sending an event requires an AXAuraObjWrapper, not an actual view, so
dispatch events on current_tree_->GetRoot() by default. This fixes a
crash in ChromeVox's mouse following where events are fired when there
is no active window (as when all windows are minimized).

Change-Id: I513d9b0547a5b31a7cf26a57648846c10bd86866
Reviewed-on: https://chromium-review.googlesource.com/c/1294517
Commit-Queue: James Wallace-Lee <jamwalla@chromium.org>
Reviewed-by: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#602030}

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

@@ -93,12 +93,11 @@ void AutomationManagerAura::HandleEvent(views::View* view,
 }
 
 void AutomationManagerAura::HandleEvent(ax::mojom::Event event_type) {
-#if defined(OS_CHROMEOS)
-  aura::Window* root_window = ash::wm::GetActiveWindow();
-  views::Widget* widget = views::Widget::GetWidgetForNativeView(root_window);
-  if (widget)
-    HandleEvent(widget->GetRootView(), event_type);
-#endif
+  views::AXAuraObjWrapper* obj = current_tree_->GetRoot();
+  if (!obj)
+    return;
+
+  AutomationManagerAura::SendEvent(obj, event_type);
 }
 
 void AutomationManagerAura::SendEventOnObjectById(int32_t id,