Use ui::AX_EVENT_SELECTION to read aloud omnibox suggestion answers.

chrome/browser/ui/views/omnibox/omnibox_result_view.cc

Index: chrome/browser/ui/views/omnibox/omnibox_result_view.cc
diff --git a/chrome/browser/ui/views/omnibox/omnibox_result_view.cc b/chrome/browser/ui/views/omnibox/omnibox_result_view.cc
index 87902bb5f48a65fae90d1cdadc908cd4206cfee3..fe4c694b634a7b603bf45585d513203d7036c142 100644
--- a/chrome/browser/ui/views/omnibox/omnibox_result_view.cc
+++ b/chrome/browser/ui/views/omnibox/omnibox_result_view.cc
@@ -296,7 +296,7 @@ void OmniboxResultView::OnSelected() {
   // updating the text in the omnibox but this alert and GetAccessibleNodeData
   // below make the answer contents accessible.
   if (match_.answer)
-    NotifyAccessibilityEvent(ui::AX_EVENT_ALERT, true);
+    NotifyAccessibilityEvent(ui::AX_EVENT_SELECTION, true);
 }
 
 gfx::Size OmniboxResultView::GetPreferredSize() const {