Add a row in the network tray to inform users to turn Bluetooth on to enable Tether.

ash/system/tray/tray_popup_item_style.cc

Index: ash/system/tray/tray_popup_item_style.cc
diff --git a/ash/system/tray/tray_popup_item_style.cc b/ash/system/tray/tray_popup_item_style.cc
index f8037850eda938537170cd284baa19a6d7a34189..97947db9203d7ca98ff4633c56507c055d262f55 100644
--- a/ash/system/tray/tray_popup_item_style.cc
+++ b/ash/system/tray/tray_popup_item_style.cc
@@ -89,6 +89,13 @@ void TrayPopupItemStyle::SetupLabel(views::Label* label) const {
       label->SetFontList(base_font_list.Derive(1, gfx::Font::NORMAL,
                                                gfx::Font::Weight::NORMAL));
       break;
+    case FontStyle::CLICKABLE_SYSTEM_INFO:
+      label->SetFontList(base_font_list.Derive(1, gfx::Font::NORMAL,
+                                               gfx::Font::Weight::NORMAL));
+      label->SetEnabledColor(label->GetNativeTheme()->GetSystemColor(
+          ui::NativeTheme::kColorId_ProminentButtonColor));
+      label->SetAutoColorReadabilityEnabled(false);
+      break;
     case FontStyle::BUTTON:
       label->SetFontList(base_font_list.Derive(0, gfx::Font::NORMAL,
                                                gfx::Font::Weight::MEDIUM));