diff -r 000000000000 -r 6474c204b198 layout/generic/nsAbsoluteContainingBlock.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/layout/generic/nsAbsoluteContainingBlock.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,145 @@
+/* -*- 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/. */
+
+/*
+ * code for managing absolutely positioned children of a rendering
+ * object that is a containing block for them
+ */
+
+#ifndef nsAbsoluteContainingBlock_h___
+#define nsAbsoluteContainingBlock_h___
+
+#include "nsFrameList.h"
+#include "nsIFrame.h"
+
+class nsContainerFrame;
+class nsHTMLReflowState;
+class nsPresContext;
+
+/**
+ * This class contains the logic for being an absolute containing block.  This
+ * class is used within viewport frames (for frames representing content with
+ * fixed position) and blocks (for frames representing absolutely positioned
+ * content), since each set of frames is absolutely positioned with respect to
+ * its parent.
+ *
+ * There is no principal child list, just a named child list which contains
+ * the absolutely positioned frames (kAbsoluteList or kFixedList).
+ *
+ * All functions include as the first argument the frame that is delegating
+ * the request.
+ */
+class nsAbsoluteContainingBlock
+{
+public:
+  typedef nsIFrame::ChildListID ChildListID;
+
+  nsAbsoluteContainingBlock(ChildListID aChildListID)
+#ifdef DEBUG
+    : mChildListID(aChildListID)
+#endif
+  {
+    MOZ_ASSERT(mChildListID == nsIFrame::kAbsoluteList ||
+               mChildListID == nsIFrame::kFixedList,
+               "should either represent position:fixed or absolute content");
+  }
+
+  const nsFrameList& GetChildList() const { return mAbsoluteFrames; }
+  void AppendChildList(nsTArray<nsIFrame::ChildList>* aLists,
+                       ChildListID aListID) const
+  {
+    NS_ASSERTION(aListID == mChildListID, "wrong list ID");
+    GetChildList().AppendIfNonempty(aLists, aListID);
+  }
+
+  nsresult SetInitialChildList(nsIFrame*       aDelegatingFrame,
+                               ChildListID     aListID,
+                               nsFrameList&    aChildList);
+  nsresult AppendFrames(nsIFrame*      aDelegatingFrame,
+                        ChildListID    aListID,
+                        nsFrameList&   aFrameList);
+  nsresult InsertFrames(nsIFrame*      aDelegatingFrame,
+                        ChildListID    aListID,
+                        nsIFrame*      aPrevFrame,
+                        nsFrameList&   aFrameList);
+  void RemoveFrame(nsIFrame*      aDelegatingFrame,
+                   ChildListID    aListID,
+                   nsIFrame*      aOldFrame);
+
+  /**
+   * Called by the delegating frame after it has done its reflow first. This
+   * function will reflow any absolutely positioned child frames that need to
+   * be reflowed, e.g., because the absolutely positioned child frame has
+   * 'auto' for an offset, or a percentage based width or height.
+   *
+   * @param aOverflowAreas, if non-null, is unioned with (in the local
+   * coordinate space) the overflow areas of the absolutely positioned
+   * children.
+   *
+   * @param aReflowStatus is assumed to be already-initialized, e.g. with the
+   * status of the delegating frame's main reflow. This function merges in the
+   * statuses of the absolutely positioned children's reflows.
+   */
+  nsresult Reflow(nsContainerFrame*        aDelegatingFrame,
+                  nsPresContext*           aPresContext,
+                  const nsHTMLReflowState& aReflowState,
+                  nsReflowStatus&          aReflowStatus,
+                  const nsRect&            aContainingBlock,
+                  bool                     aConstrainHeight,
+                  bool                     aCBWidthChanged,
+                  bool                     aCBHeightChanged,
+                  nsOverflowAreas*         aOverflowAreas);
+
+  void DestroyFrames(nsIFrame* aDelegatingFrame,
+                     nsIFrame* aDestructRoot);
+
+  bool HasAbsoluteFrames() const { return mAbsoluteFrames.NotEmpty(); }
+
+  /**
+   * Mark our size-dependent absolute frames with NS_FRAME_HAS_DIRTY_CHILDREN
+   * so that we'll make sure to reflow them.
+   */
+  void MarkSizeDependentFramesDirty();
+
+  /**
+   * Mark all our absolute frames with NS_FRAME_IS_DIRTY.
+   */
+  void MarkAllFramesDirty();
+
+protected:
+  /**
+   * Returns true if the position of aFrame depends on the position of
+   * its placeholder or if the position or size of aFrame depends on a
+   * containing block dimension that changed.
+   */
+  bool FrameDependsOnContainer(nsIFrame* aFrame, bool aCBWidthChanged,
+                               bool aCBHeightChanged);
+
+  nsresult ReflowAbsoluteFrame(nsIFrame*                aDelegatingFrame,
+                               nsPresContext*           aPresContext,
+                               const nsHTMLReflowState& aReflowState,
+                               const nsRect&            aContainingBlockRect,
+                               bool                     aConstrainHeight,
+                               nsIFrame*                aKidFrame,
+                               nsReflowStatus&          aStatus,
+                               nsOverflowAreas*         aOverflowAreas);
+
+  /**
+   * Mark our absolute frames dirty.
+   * @param aMarkAllDirty if true, all will be marked with NS_FRAME_IS_DIRTY.
+   * Otherwise, the size-dependant ones will be marked with
+   * NS_FRAME_HAS_DIRTY_CHILDREN.
+   */
+  void DoMarkFramesDirty(bool aMarkAllDirty);
+
+protected:
+  nsFrameList mAbsoluteFrames;  // additional named child list
+
+#ifdef DEBUG
+  ChildListID const mChildListID; // kFixedList or kAbsoluteList
+#endif
+};
+
+#endif /* nsnsAbsoluteContainingBlock_h___ */