Allow the user to cancel the capture region action, and show its active status in the tray.

ash/utility/screenshot_controller.h

Index: ash/utility/screenshot_controller.h
diff --git a/ash/utility/screenshot_controller.h b/ash/utility/screenshot_controller.h
index 676ed9e9c10811815d188bef9e79ea5425a9e0f8..8416bbd3d2731dcf0334d87e81caa4bc358a2a52 100644
--- a/ash/utility/screenshot_controller.h
+++ b/ash/utility/screenshot_controller.h
@@ -54,6 +54,9 @@ class ASH_EXPORT ScreenshotController : public ui::EventHandler,
   // Starts the UI for taking a window screenshot;
   void StartWindowScreenshotSession(ScreenshotDelegate* screenshot_delegate);
 
+  // Cancels any active screenshot session.
+  void CancelScreenshotSession();
+
   // If set to true, then only events generated by a pen can be used to select
   // the area to take a screenshot of. This is reset to false after a screenshot
   // operation is completed.
@@ -78,7 +81,6 @@ class ASH_EXPORT ScreenshotController : public ui::EventHandler,
   void MaybeStart(const ui::LocatedEvent& event);
   void CompleteWindowScreenshot();
   void CompletePartialScreenshot();
-  void Cancel();
   void Update(const ui::LocatedEvent& event);
   void UpdateSelectedWindow(ui::LocatedEvent* event);
   void SetSelectedWindow(aura::Window* window);