Clean up some ash constants.

ash/system/tray/tray_utils.cc

Index: ash/system/tray/tray_utils.cc
diff --git a/ash/system/tray/tray_utils.cc b/ash/system/tray/tray_utils.cc
index baf8fa9608aa9bd03844fb72c276fb48bf9ae26b..6b60b1256872e8cdfb3d334bf8dc8a6edac49b5a 100644
--- a/ash/system/tray/tray_utils.cc
+++ b/ash/system/tray/tray_utils.cc
@@ -4,6 +4,7 @@
 
 #include "ash/system/tray/tray_utils.h"
 
+#include "ash/system/tray/tray_constants.h"
 #include "ui/gfx/font_list.h"
 #include "ui/views/controls/label.h"
 
@@ -13,8 +14,8 @@ void SetupLabelForTray(views::Label* label) {
   // The text is drawn on an transparent bg, so we must disable subpixel
   // rendering.
   label->SetSubpixelRenderingEnabled(false);
-  label->SetFontList(
-      gfx::FontList().Derive(2, gfx::Font::NORMAL, gfx::Font::Weight::MEDIUM));
+  label->SetFontList(gfx::FontList().Derive(
+      kTrayTextFontSizeIncrease, gfx::Font::NORMAL, gfx::Font::Weight::MEDIUM));
 }
 
 }  // namespace ash