Add UMA stats for pen palette

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

Index: ash/common/system/chromeos/palette/common_palette_tool.h
diff --git a/ash/common/system/chromeos/palette/common_palette_tool.h b/ash/common/system/chromeos/palette/common_palette_tool.h
index 67ef66fc23c22482f24e64bf1702f2db047dcab5..0e148acafb1e9fe8f0e3e54626c1325eea1da5ec 100644
--- a/ash/common/system/chromeos/palette/common_palette_tool.h
+++ b/ash/common/system/chromeos/palette/common_palette_tool.h
@@ -9,6 +9,7 @@
 #include "ash/common/system/tray/hover_highlight_view.h"
 #include "ash/common/system/tray/view_click_listener.h"
 #include "base/strings/string16.h"
+#include "base/time/time.h"
 #include "ui/gfx/vector_icons_public.h"
 
 namespace ash {
@@ -37,6 +38,7 @@ class CommonPaletteTool : public PaletteTool, public ash::ViewClickListener {
 
  private:
   HoverHighlightView* highlight_view_ = nullptr;
+  base::TimeTicks start_time_;

[jdufault, 2016/09/02 21:54:30]

Add a comment, maybe something like

// When the tool last became active. Used for recording UMA metrics.

[jdufault, 2016/09/02 21:54:30]

Can we use base::Time?

[Ilya Sherman, 2016/09/02 22:02:49]

base::Time is susceptible to timezone changes, etc.  base::TimeTicks is
generally preferred for measuring durations.

[xiaoyinh(OOO Sep 11-29), 2016/09/06 17:40:05]

Done.

 
   DISALLOW_COPY_AND_ASSIGN(CommonPaletteTool);
 };