[Mac] Confirm-to-quit: Add histogram metrics.

chrome/browser/ui/cocoa/confirm_quit_panel_controller.h

Index: chrome/browser/ui/cocoa/confirm_quit_panel_controller.h
diff --git a/chrome/browser/ui/cocoa/confirm_quit_panel_controller.h b/chrome/browser/ui/cocoa/confirm_quit_panel_controller.h
index 88b66f3044155160ab10b7f69117c323c29efbaa..8a1816d45a779112fedb58890c9bf5674a560dcc 100644
--- a/chrome/browser/ui/cocoa/confirm_quit_panel_controller.h
+++ b/chrome/browser/ui/cocoa/confirm_quit_panel_controller.h
@@ -12,6 +12,26 @@
 
 @class ConfirmQuitFrameView;
 
+namespace confirm_quit {
+
+enum ConfirmQuitMetric {
+  // The user quit without having the feature enabled.
+  kNoConfirm = 0,
+  // The user held Cmd+Q for the entire duration.
+  kHoldDuration,
+  // The user hit Cmd+Q twice for the accelerated path.
+  kDoubleTap,
+  // The user tapped Cmd+Q once and then held it.
+  kTapHold,
+
+  kSampleCount
+};
+
+// Records the histogram value for the above metric.
+void RecordHistogram(ConfirmQuitMetric sample);
+
+}  // namespace confirm_quit
+
 // The ConfirmQuitPanelController manages the black HUD window that tells users
 // to "Hold Cmd+Q to Quit".
 @interface ConfirmQuitPanelController : NSWindowController<NSWindowDelegate> {