Add UMA stats for pen palette

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

Index: ash/common/system/chromeos/palette/palette_ids.cc
diff --git a/ash/common/system/chromeos/palette/palette_ids.cc b/ash/common/system/chromeos/palette/palette_ids.cc
index 5d5f48510d7e1d758636f06c617f00010fd182ff..fccc2048716aad918515984ebf9e3cbb958f394d 100644
--- a/ash/common/system/chromeos/palette/palette_ids.cc
+++ b/ash/common/system/chromeos/palette/palette_ids.cc
@@ -39,4 +39,29 @@ std::string PaletteGroupToString(PaletteGroup group) {
   return std::string();
 }
 
+PaletteTrayOptions PaletteToolIdToPaletteTrayOptions(PaletteToolId tool_id) {
+  PaletteTrayOptions option = PALETTE_OPTIONS_COUNT;

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

Can we just return the value directly?

switch (tool_id) {
  case PaletteToolId::CREATE_NOTE:
    return PALETTE_NEW_NOTE;
  // ...
}

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

Done.

+  switch (tool_id) {
+    case PaletteToolId::NONE:
+      break;
+    case PaletteToolId::CREATE_NOTE:
+      option = PALETTE_NEW_NOTE;
+      break;
+    case PaletteToolId::CAPTURE_REGION:
+      option = PALETTE_CAPTURE_REGION;
+      break;
+    case PaletteToolId::CAPTURE_SCREEN:
+      option = PALETTE_CAPTURE_SCREEN;
+      break;
+    case PaletteToolId::LASER_POINTER:
+      option = PALETTE_LASER_POINTER;
+      break;
+    case PaletteToolId::MAGNIFY:
+      option = PALETTE_MAGNIFY;
+      break;
+  }
+
+  return option;
+}
+
 }  // namespace ash