UMA stats for stylus usage

ui/aura/client/aura_constants.h

Index: ui/aura/client/aura_constants.h
diff --git a/ui/aura/client/aura_constants.h b/ui/aura/client/aura_constants.h
index a177f256bb0bc8fb35539b5fa4efdcf6299dce85..1ce2e67d8f2e83f9aa6216b7e34ffe12c1615419 100644
--- a/ui/aura/client/aura_constants.h
+++ b/ui/aura/client/aura_constants.h
@@ -69,6 +69,11 @@ AURA_EXPORT extern const WindowProperty<ui::WindowShowState>* const
 AURA_EXPORT extern const WindowProperty<ui::WindowShowState>* const
     kShowStateKey;
 
+// A property key to store the type of window that will be used to record stylus
+// metrics.
+AURA_EXPORT extern const aura::WindowProperty<int>* const

[xiyuan, 2016/09/12 20:15:47]

This does not feel like need to be here. Can we move this somewhere else, e.g.
in stylus_metrics_recorder.h ? 

[xiaoyinh(OOO Sep 11-29), 2016/09/16 18:41:16]

Done.

+    kStylusWindowTypeBucket;
+
 // The inset of the topmost view in the client view from the top of the
 // non-client view. The topmost view depends on the window type. The topmost
 // view is the tab strip for tabbed browser windows, the toolbar for popups,