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

ash/utility/screenshot_controller.h

 // Copyright 2014 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 ASH_UTILITY_SCREENSHOT_CONTROLLER_H_
 #define ASH_UTILITY_SCREENSHOT_CONTROLLER_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 36 matching lines @@
   // delete the returned values. |draw_overlay_immediately| controls if the grey
   // overlay will be drawn immediately. If false, then the overlay will be drawn
   // only after the user has started creating the clipping rect for the
   // screenshot.
   void StartPartialScreenshotSession(ScreenshotDelegate* screenshot_delegate,
                                      bool draw_overlay_immediately);
 
   // 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.
   void set_pen_events_only(bool pen_events_only) {
     pen_events_only_ = pen_events_only;
   }
   bool pen_events_only() const { return pen_events_only_; }
 
  private:
   enum Mode {
     NONE,
     PARTIAL,
     WINDOW,
   };
 
   friend class ScreenshotControllerTest;
 
   class ScopedCursorSetter;
   class ScreenshotLayer;
 
   // Starts, ends, cancels, or updates the region selection.
   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);
 
   // Returns true if the event should be processed.
   bool ShouldProcessEvent(const ui::PointerDetails& pointer_details) const;
 
   // ui::EventHandler:
   void OnKeyEvent(ui::KeyEvent* event) override;
   void OnMouseEvent(ui::MouseEvent* event) override;
@@ skipping 29 matching lines @@
 
   // ScreenshotDelegate to take the actual screenshot. No ownership.
   ScreenshotDelegate* screenshot_delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenshotController);
 };
 
 }  // namespace ash
 
 #endif  // ASH_UTILITY_SCREENSHOT_CONTROLLER_H_