Fix incorrect use of AXState caused when refactoring two enums into one.

ash/system/tray/hover_highlight_view.cc

Index: ash/system/tray/hover_highlight_view.cc
diff --git a/ash/system/tray/hover_highlight_view.cc b/ash/system/tray/hover_highlight_view.cc
index bc8f017ab7aa3b98c92129696ed0f113014f92cb..e78944cc9a56074a8f177bc1dffaf72124ca7aed 100644
--- a/ash/system/tray/hover_highlight_view.cc
+++ b/ash/system/tray/hover_highlight_view.cc
@@ -142,7 +142,8 @@ void HoverHighlightView::GetAccessibleState(ui::AXViewState* state) {
 
   if (checkable_) {
     state->role = ui::AX_ROLE_CHECK_BOX;
-    state->state = checked_ ? ui::AX_STATE_CHECKED : 0;
+    if (checked_)
+      state->AddStateFlag(ui::AX_STATE_CHECKED);
   }
 }