Add UMA stats for pen palette

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

Index: ash/common/system/chromeos/palette/palette_tool_manager.h
diff --git a/ash/common/system/chromeos/palette/palette_tool_manager.h b/ash/common/system/chromeos/palette/palette_tool_manager.h
index 798624803784dff32ec90a2cead66a28f27c5760..32deb0d7cc804f06848e6d696fd0f247be1347e5 100644
--- a/ash/common/system/chromeos/palette/palette_tool_manager.h
+++ b/ash/common/system/chromeos/palette/palette_tool_manager.h
@@ -48,6 +48,9 @@ class ASH_EXPORT PaletteToolManager : public PaletteTool::Delegate {
     // Return the window associated with this palette.
     virtual WmWindow* GetWindow() = 0;
 
+    // Record usage of each pen palette option.
+    virtual void RecordPaletteMetrics(ash::PaletteTrayOptions option) = 0;
+
    private:
     DISALLOW_COPY_AND_ASSIGN(Delegate);
   };
@@ -90,6 +93,7 @@ class ASH_EXPORT PaletteToolManager : public PaletteTool::Delegate {
   void DisableTool(PaletteToolId tool_id) override;
   void HidePalette() override;
   WmWindow* GetWindow() override;
+  void RecordPaletteMetrics(ash::PaletteTrayOptions option) override;
 
   PaletteTool* FindToolById(PaletteToolId tool_id);