diff -r 000000000000 -r 6474c204b198 gfx/layers/apz/util/APZCCallbackHelper.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gfx/layers/apz/util/APZCCallbackHelper.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,103 @@
+/* -*- 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/. */
+
+#ifndef mozilla_layers_APZCCallbackHelper_h
+#define mozilla_layers_APZCCallbackHelper_h
+
+#include "FrameMetrics.h"
+#include "nsIContent.h"
+#include "nsIDocument.h"
+#include "nsIDOMWindowUtils.h"
+
+namespace mozilla {
+namespace layers {
+
+/* This class contains some helper methods that facilitate implementing the
+   GeckoContentController callback interface required by the AsyncPanZoomController.
+   Since different platforms need to implement this interface in similar-but-
+   not-quite-the-same ways, this utility class provides some helpful methods
+   to hold code that can be shared across the different platform implementations.
+ */
+class APZCCallbackHelper
+{
+    typedef mozilla::layers::FrameMetrics FrameMetrics;
+    typedef mozilla::layers::ScrollableLayerGuid ScrollableLayerGuid;
+
+public:
+    /* Checks to see if the pres shell that the given FrameMetrics object refers
+       to is still the valid pres shell for the DOMWindowUtils. This can help
+       guard against apply stale updates (updates meant for a pres shell that has
+       since been torn down and replaced). */
+    static bool HasValidPresShellId(nsIDOMWindowUtils* aUtils,
+                                    const FrameMetrics& aMetrics);
+
+    /* Applies the scroll and zoom parameters from the given FrameMetrics object to
+       the root frame corresponding to the given DOMWindowUtils. If tiled thebes
+       layers are enabled, this will align the displayport to tile boundaries.
+       Setting the scroll position can cause some small adjustments to be made
+       to the actual scroll position. aMetrics' display port and scroll position
+       will be updated with any modifications made. */
+    static void UpdateRootFrame(nsIDOMWindowUtils* aUtils,
+                                FrameMetrics& aMetrics);
+
+    /* Applies the scroll parameters from the given FrameMetrics object to the subframe
+       corresponding to the given content object. If tiled thebes
+       layers are enabled, this will align the displayport to tile boundaries.
+       Setting the scroll position can cause some small adjustments to be made
+       to the actual scroll position. aMetrics' display port and scroll position
+       will be updated with any modifications made. */
+    static void UpdateSubFrame(nsIContent* aContent,
+                               FrameMetrics& aMetrics);
+
+    /* Get the DOMWindowUtils for the window corresponding to the given document. */
+    static already_AddRefed<nsIDOMWindowUtils> GetDOMWindowUtils(const nsIDocument* aDoc);
+
+    /* Get the DOMWindowUtils for the window corresponding to the givent content
+       element. This might be an iframe inside the tab, for instance. */
+    static already_AddRefed<nsIDOMWindowUtils> GetDOMWindowUtils(const nsIContent* aContent);
+
+    /* Get the presShellId and view ID for the given content element, if they can be
+       found. Returns false if the values could not be found, true if they could. */
+    static bool GetScrollIdentifiers(const nsIContent* aContent,
+                                     uint32_t* aPresShellIdOut,
+                                     FrameMetrics::ViewID* aViewIdOut);
+
+    /* Tell layout that we received the scroll offset update for the given view ID, so
+       that it accepts future scroll offset updates from APZ. */
+    static void AcknowledgeScrollUpdate(const FrameMetrics::ViewID& aScrollId,
+                                        const uint32_t& aScrollGeneration);
+
+    /* Save an "input transform" property on the content element corresponding to
+       the scrollable content. This is needed because in some cases when the APZ code
+       sends a paint request via the GeckoContentController interface, we don't always
+       apply the scroll offset that was requested. Since the APZ code doesn't know
+       that we didn't apply it, it will transform inputs assuming that we had applied
+       it, and so we need to apply a fixup to the input to account for the fact that
+       we didn't.
+       The |aApzcMetrics| argument are the metrics that the APZ sent us, and the
+       |aActualMetrics| argument are the metrics representing the gecko state after we
+       applied some or all of the APZ metrics. */
+    static void UpdateCallbackTransform(const FrameMetrics& aApzcMetrics,
+                                        const FrameMetrics& aActualMetrics);
+
+    /* Apply an "input transform" to the given |aInput| and return the transformed value.
+       The input transform applied is the one for the content element corresponding to
+       |aGuid|; this is populated in a previous call to UpdateCallbackTransform. See that
+       method's documentations for details. */
+    static CSSPoint ApplyCallbackTransform(const CSSPoint& aInput,
+                                           const ScrollableLayerGuid& aGuid);
+
+    /* Same as above, but operates on nsIntPoint that are assumed to be in LayoutDevice
+       pixel space. Requires an additonal |aScale| parameter to convert between CSS and
+       LayoutDevice space. */
+    static nsIntPoint ApplyCallbackTransform(const nsIntPoint& aPoint,
+                                             const ScrollableLayerGuid& aGuid,
+                                             const CSSToLayoutDeviceScale& aScale);
+};
+
+}
+}
+
+#endif /* mozilla_layers_APZCCallbackHelper_h */