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

chrome/browser/ui/cocoa/confirm_quit_panel_controller.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_UI_COCOA_CONFIRM_QUIT_PANEL_CONTROLLER_H_
 #define CHROME_BROWSER_UI_COCOA_CONFIRM_QUIT_PANEL_CONTROLLER_H_
 
 #import <Cocoa/Cocoa.h>
 
 #import "base/mac/cocoa_protocols.h"
 #include "ui/base/models/accelerator_cocoa.h"
 
 @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> {
  @private
   // The content view of the window that this controller manages.
   ConfirmQuitFrameView* contentView_;  // Weak, owned by the window.
 }
 
 // Returns a singleton instance of the Controller. This will create one if it
 // does not currently exist.
@@ skipping 20 matching lines @@
 // Returns a string representation fit for display of |+quitAccelerator|.
 + (NSString*)keyCommandString;
 
 @end
 
 @interface ConfirmQuitPanelController (UnitTesting)
 + (NSString*)keyCombinationForAccelerator:(const ui::AcceleratorCocoa&)item;
 @end
 
 #endif  // CHROME_BROWSER_UI_COCOA_CONFIRM_QUIT_PANEL_CONTROLLER_H_