diff -r 000000000000 -r 6474c204b198 widget/nsITaskbarPreviewController.idl
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/widget/nsITaskbarPreviewController.idl	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,92 @@
+/* vim: se cin sw=2 ts=2 et : */
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+interface nsIDocShell;
+interface nsITaskbarPreview;
+interface nsITaskbarPreviewButton;
+
+/**
+ * nsITaskbarPreviewController
+ *
+ * nsITaskbarPreviewController provides the behavior for the taskbar previews.
+ * Its methods and properties are used by nsITaskbarPreview. Clients are
+ * intended to provide their own implementation of this interface. Depending on
+ * the interface the controller is attached to, only certain methods/attributes
+ * are required to be implemented.
+ */
+[scriptable, uuid(4FC0AFBB-3E22-4FBA-AC21-953350AF0411)]
+interface nsITaskbarPreviewController : nsISupports
+{
+  /**
+   * The width of the preview image. This value is allowed to change at any
+   * time. See drawPreview for more information.
+   */
+  readonly attribute unsigned long width;
+
+  /**
+   * The height of the preview image. This value is allowed to change at any
+   * time.  See drawPreview for more information.
+   */
+  readonly attribute unsigned long height;
+
+  /**
+   * The aspect ratio of the thumbnail - this does not need to match the ratio
+   * of the preview. This value is allowed to change at any time. See
+   * drawThumbnail for more information.
+   */
+  readonly attribute float thumbnailAspectRatio;
+
+  /**
+   * Invoked by nsITaskbarPreview when it needs to render the preview. The
+   * context is attached to a surface with the controller's width and height
+   * which are obtained immediately before the call.
+   *
+   * Note that the context is not attached to a canvas element.
+   *
+   * @param ctx Canvas drawing context
+   */
+  boolean drawPreview(in nsISupports ctx);
+
+  /**
+   * Invoked by the taskbar preview when it needs to draw the thumbnail in the
+   * taskbar's application preview window.
+   *
+   * Note: it is guaranteed that width/height == thumbnailAspectRatio
+   * (modulo rounding errors)
+   *
+   * Also note that the context is not attached to a canvas element.
+   *
+   * @param ctx Canvas drawing context
+   * @param width The width of the surface backing the drawing context
+   * @param height The height of the surface backing the drawing context
+   */
+  boolean drawThumbnail(in nsISupports ctx, in unsigned long width, in unsigned long height);
+
+  /**
+   * Invoked when the user presses the close button on the tab preview.
+   */
+  void onClose();
+
+  /**
+   * Invoked when the user clicks on the tab preview.
+   *
+   * @return true if the top level window corresponding to the preview should
+   *         be activated, false if activation is not accepted.
+   */
+  boolean onActivate();
+
+  /**
+   * Invoked when one of the buttons on the window preview's toolbar is pressed.
+   *
+   * @param button The button that was pressed. This can be compared with the
+   *               buttons returned by nsITaskbarWindowPreview.getButton.
+   */
+  void onClick(in nsITaskbarPreviewButton button);
+};
+