diff -r 000000000000 -r 6474c204b198 layout/generic/nsViewportFrame.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/layout/generic/nsViewportFrame.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,99 @@
+/* -*- 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/. */
+
+/*
+ * rendering object that is the root of the frame tree, which contains
+ * the document's scrollbars and contains fixed-positioned elements
+ */
+
+#ifndef nsViewportFrame_h___
+#define nsViewportFrame_h___
+
+#include "mozilla/Attributes.h"
+#include "nsContainerFrame.h"
+
+class nsPresContext;
+
+/**
+  * ViewportFrame is the parent of a single child - the doc root frame or a scroll frame 
+  * containing the doc root frame. ViewportFrame stores this child in its primary child 
+  * list.
+  */
+class ViewportFrame : public nsContainerFrame {
+public:
+  NS_DECL_QUERYFRAME_TARGET(ViewportFrame)
+  NS_DECL_QUERYFRAME
+  NS_DECL_FRAMEARENA_HELPERS
+
+  typedef nsContainerFrame Super;
+
+  ViewportFrame(nsStyleContext* aContext)
+    : nsContainerFrame(aContext)
+  {}
+  virtual ~ViewportFrame() { } // useful for debugging
+
+  virtual void Init(nsIContent*      aContent,
+                    nsIFrame*        aParent,
+                    nsIFrame*        asPrevInFlow) MOZ_OVERRIDE;
+
+  virtual nsresult SetInitialChildList(ChildListID     aListID,
+                                       nsFrameList&    aChildList) MOZ_OVERRIDE;
+
+  virtual nsresult AppendFrames(ChildListID     aListID,
+                                nsFrameList&    aFrameList) MOZ_OVERRIDE;
+
+  virtual nsresult InsertFrames(ChildListID     aListID,
+                                nsIFrame*       aPrevFrame,
+                                nsFrameList&    aFrameList) MOZ_OVERRIDE;
+
+  virtual nsresult RemoveFrame(ChildListID     aListID,
+                               nsIFrame*       aOldFrame) MOZ_OVERRIDE;
+
+  virtual void BuildDisplayList(nsDisplayListBuilder*   aBuilder,
+                                const nsRect&           aDirtyRect,
+                                const nsDisplayListSet& aLists) MOZ_OVERRIDE;
+
+  virtual nscoord GetMinWidth(nsRenderingContext *aRenderingContext) MOZ_OVERRIDE;
+  virtual nscoord GetPrefWidth(nsRenderingContext *aRenderingContext) MOZ_OVERRIDE;
+  virtual nsresult Reflow(nsPresContext*          aPresContext,
+                          nsHTMLReflowMetrics&     aDesiredSize,
+                          const nsHTMLReflowState& aReflowState,
+                          nsReflowStatus&          aStatus) MOZ_OVERRIDE;
+
+  /**
+   * Get the "type" of the frame
+   *
+   * @see nsGkAtoms::viewportFrame
+   */
+  virtual nsIAtom* GetType() const MOZ_OVERRIDE;
+
+  /**
+   * Adjust aReflowState to account for scrollbars and pres shell
+   * GetScrollPositionClampingScrollPortSizeSet and
+   * GetContentDocumentFixedPositionMargins adjustments.
+   * @return the rect to use as containing block rect
+   */
+  nsRect AdjustReflowStateAsContainingBlock(nsHTMLReflowState* aReflowState) const;
+
+#ifdef DEBUG_FRAME_DUMP
+  virtual nsresult GetFrameName(nsAString& aResult) const MOZ_OVERRIDE;
+#endif
+
+private:
+  virtual mozilla::layout::FrameChildListID GetAbsoluteListID() const MOZ_OVERRIDE { return kFixedList; }
+
+protected:
+  /**
+   * Calculate how much room is available for fixed frames. That means
+   * determining if the viewport is scrollable and whether the vertical and/or
+   * horizontal scrollbars are visible.  Adjust the computed width/height and
+   * available width for aReflowState accordingly.
+   * @return the current scroll position, or 0,0 if not scrollable
+   */
+  nsPoint AdjustReflowStateForScrollbars(nsHTMLReflowState* aReflowState) const;
+};
+
+
+#endif // nsViewportFrame_h___