Add UMA stats for pen palette

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

Index: ash/common/system/chromeos/palette/palette_tray.cc
diff --git a/ash/common/system/chromeos/palette/palette_tray.cc b/ash/common/system/chromeos/palette/palette_tray.cc
index 80ecc3bb8117eda76ff491066ee15d2dd80d69b0..3710d9ab82d7920044c1383847bcb3674d909f72 100644
--- a/ash/common/system/chromeos/palette/palette_tray.cc
+++ b/ash/common/system/chromeos/palette/palette_tray.cc
@@ -18,6 +18,7 @@
 #include "ash/common/wm_root_window_controller.h"
 #include "ash/common/wm_shell.h"
 #include "ash/common/wm_window.h"
+#include "base/metrics/histogram.h"

[Ilya Sherman, 2016/09/02 21:39:30]

nit: histogram_macros

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

Done.

 #include "grit/ash_resources.h"
 #include "grit/ash_strings.h"
 #include "ui/base/l10n/l10n_util.h"
@@ -108,9 +109,13 @@ class TitleView : public views::View, public views::ButtonListener {
   // views::ButtonListener:
   void ButtonPressed(views::Button* sender, const ui::Event& event) override {
     if (sender == settings_button_) {
+      palette_tray_->RecordPaletteMetrics(
+          ash::PaletteTrayOptions::PALETTE_SETTINGS_BUTTON);
       WmShell::Get()->system_tray_delegate()->ShowPaletteSettings();

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

ShowPaletteSettings should already be recording a metric ("ShowPaletteOptions"
to be precise).

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

Should I remove mine if that's case? It might still be useful as
"ShowPaletteOptions" is recorded as user-action, and here we can compare 
PALETTE_SETTINGS_BUTTON with all other options side by side?

       palette_tray_->HidePalette();
     } else if (sender == help_button_) {
+      palette_tray_->RecordPaletteMetrics(
+          ash::PaletteTrayOptions::PALETTE_HELP_BUTTON);
       WmShell::Get()->system_tray_delegate()->ShowPaletteHelp();
       palette_tray_->HidePalette();
     } else {
@@ -173,7 +178,10 @@ PaletteTray::~PaletteTray() {
 
 bool PaletteTray::PerformAction(const ui::Event& event) {
   if (bubble_) {
-    bubble_.reset();
+    if (num_actions_in_palette == 0) {
+      RecordPaletteMetrics(ash::PaletteTrayOptions::PALETTE_CLOSED_NO_ACTION);
+    }
+    HidePalette();
     return true;
   }
 
@@ -236,7 +244,9 @@ void PaletteTray::OnLockStateChanged(bool locked) {
 }
 
 void PaletteTray::ClickedOutsideBubble() {
-  bubble_.reset();
+  if (num_actions_in_palette == 0)
+    RecordPaletteMetrics(ash::PaletteTrayOptions::PALETTE_CLOSED_NO_ACTION);
+  HidePalette();
 }
 
 base::string16 PaletteTray::GetAccessibleNameForTray() {
@@ -245,7 +255,7 @@ base::string16 PaletteTray::GetAccessibleNameForTray() {
 
 void PaletteTray::HideBubbleWithView(const views::TrayBubbleView* bubble_view) {
   if (bubble_->bubble_view() == bubble_view)
-    bubble_.reset();
+    HidePalette();
 }
 
 void PaletteTray::BubbleViewDestroyed() {
@@ -303,14 +313,29 @@ void PaletteTray::HideBubble(const views::TrayBubbleView* bubble_view) {
 }
 
 void PaletteTray::HidePalette() {
+  is_palette_auto_opened = false;
+  num_actions_in_palette = 0;
   bubble_.reset();
 }
 
+void PaletteTray::RecordPaletteMetrics(ash::PaletteTrayOptions option) {
+  if (option == ash::PaletteTrayOptions::PALETTE_OPTIONS_COUNT)

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

Do we want to DCHECK on this?

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

Added. Thanks

+    return;
+
+  if (is_palette_auto_opened)

[Ilya Sherman, 2016/09/02 21:39:30]

nit: Please use curly braces, since the body spans multiple lines of text

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

nit: add {} for both if/else

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

Done.

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

Done.

+    UMA_HISTOGRAM_ENUMERATION("Ash.Shelf.PaletteUsage.AutoOpened", option,
+                              ash::PaletteTrayOptions::PALETTE_OPTIONS_COUNT);
+  else
+    UMA_HISTOGRAM_ENUMERATION("Ash.Shelf.PaletteUsage", option,
+                              ash::PaletteTrayOptions::PALETTE_OPTIONS_COUNT);
+}
+
 bool PaletteTray::ShouldBlockShelfAutoHide() const {
   return !!bubble_;
 }
 
 void PaletteTray::OnActiveToolChanged() {
+  ++num_actions_in_palette;
   UpdateTrayIcon();
 }
 
@@ -353,10 +378,12 @@ void PaletteTray::OnStylusStateChanged(ui::StylusState stylus_state) {
   if (!WmShell::Get()->palette_delegate()->ShouldAutoOpenPalette())
     return;
 
-  if (stylus_state == ui::StylusState::REMOVED && !bubble_)
+  if (stylus_state == ui::StylusState::REMOVED && !bubble_) {
+    is_palette_auto_opened = true;
     ShowPalette();
-  else if (stylus_state == ui::StylusState::INSERTED && bubble_)
-    bubble_.reset();
+  } else if (stylus_state == ui::StylusState::INSERTED && bubble_) {
+    HidePalette();
+  }
 }
 
 void PaletteTray::OnPaletteEnabledPrefChanged(bool enabled) {