Add UMA stats for pen palette

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

Index: ash/common/system/chromeos/palette/palette_ids.h
diff --git a/ash/common/system/chromeos/palette/palette_ids.h b/ash/common/system/chromeos/palette/palette_ids.h
index 31dfe1323b3a674d1e686637f8241cd5fb770250..5d32ed6026f70e7e1249726e5f0c6686ac25e174 100644
--- a/ash/common/system/chromeos/palette/palette_ids.h
+++ b/ash/common/system/chromeos/palette/palette_ids.h
@@ -11,6 +11,30 @@
 
 namespace ash {
 
+// Usage of each pen palette option. This enum is used to back an UMA histogram
+// and should be treated as append-only.
+enum PaletteTrayOptions {

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

nit: Put these after either PaletteToolId or PaletteGroupIdToString() 

When reading I think PaletteGroup / PaletteToolId are more important for
conceptual understanding.

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

Done.

+  PALETTE_CLOSED_NO_ACTION = 0,
+  PALETTE_SETTINGS_BUTTON,
+  PALETTE_HELP_BUTTON,
+  PALETTE_CAPTURE_REGION,
+  PALETTE_CAPTURE_SCREEN,
+  PALETTE_NEW_NOTE,
+  PALETTE_MAGNIFY,
+  PALETTE_LASER_POINTER,
+  PALETTE_OPTIONS_COUNT
+};
+
+// Type of palette mode cancellation. This enum is used to back an UMA histogram
+// and should be treated as append-only.
+enum PaletteModeCancelType {
+  PALETTE_MODE_LASER_POINTER_CANCELLED = 0,
+  PALETTE_MODE_LASER_POINTER_SWITCHED,
+  PALETTE_MODE_MAGNIFY_CANCELLED,
+  PALETTE_MODE_MAGNIFY_SWITCHED,
+  PALETTE_MODE_CANCEL_TYPE_COUNT
+};
+
 // Palette tools are grouped into different categories. Each tool corresponds to
 // exactly one group, and at most one tool can be active per group. Actions are
 // actions the user wants to do, such as take a screenshot, and modes generally
@@ -31,6 +55,10 @@ enum class PaletteToolId {
 ASH_EXPORT std::string PaletteToolIdToString(PaletteToolId tool_id);
 ASH_EXPORT std::string PaletteGroupToString(PaletteGroup group);
 
+// Helper functions that convert PaletteToolIds to PaletteTrayOptions.
+ASH_EXPORT PaletteTrayOptions
+PaletteToolIdToPaletteTrayOptions(PaletteToolId tool_id);
+
 }  // namespace ash
 
 #endif  // ASH_COMMON_SYSTEM_CHROMEOS_PALETTE_PALETTE_IDS_H_