Add UMA stats for pen palette

ash/common/system/chromeos/palette/palette_tool.h

Index: ash/common/system/chromeos/palette/palette_tool.h
diff --git a/ash/common/system/chromeos/palette/palette_tool.h b/ash/common/system/chromeos/palette/palette_tool.h
index eaa5ff8821089db6cd745a0ec4781bb005aec9c4..261b193c130cd034f786652606abda3696c510b8 100644
--- a/ash/common/system/chromeos/palette/palette_tool.h
+++ b/ash/common/system/chromeos/palette/palette_tool.h
@@ -10,6 +10,7 @@
 #include <vector>
 
 #include "ash/ash_export.h"
+#include "ash/common/system/chromeos/palette/palette_ids.h"
 #include "base/callback.h"
 #include "base/macros.h"
 #include "ui/gfx/vector_icon_types.h"
@@ -48,6 +49,9 @@ class ASH_EXPORT PaletteTool {
     // Returns the root window.
     virtual WmWindow* GetWindow() = 0;
 
+    // Record usage of each pen palette option.
+    virtual void RecordPaletteMetrics(ash::PaletteTrayOptions option) = 0;
+
    private:
     DISALLOW_COPY_AND_ASSIGN(Delegate);
   };