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diff --git a/layout/generic/nsSplittableFrame.h b/layout/generic/nsSplittableFrame.h
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+++ b/layout/generic/nsSplittableFrame.h
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+/* -*- 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/. */
+
+/*
+ * base class for rendering objects that can be split across lines,
+ * columns, or pages
+ */
+
+#ifndef nsSplittableFrame_h___
+#define nsSplittableFrame_h___
+
+#include "mozilla/Attributes.h"
+#include "nsFrame.h"
+
+// Derived class that allows splitting
+class nsSplittableFrame : public nsFrame
+{
+public:
+  NS_DECL_ABSTRACT_FRAME(nsSplittableFrame)
+
+  virtual void Init(nsIContent*       aContent,
+                    nsContainerFrame* aParent,
+                    nsIFrame*         aPrevInFlow) override;
+  
+  virtual nsSplittableType GetSplittableType() const override;
+
+  virtual void DestroyFrom(nsIFrame* aDestructRoot) override;
+
+  /*
+   * Frame continuations can be either fluid or not:
+   * Fluid continuations ("in-flows") are the result of line breaking, 
+   * column breaking, or page breaking.
+   * Other (non-fluid) continuations can be the result of BiDi frame splitting.
+   * A "flow" is a chain of fluid continuations.
+   */
+  
+  // Get the previous/next continuation, regardless of its type (fluid or non-fluid).
+  virtual nsIFrame* GetPrevContinuation() const override;
+  virtual nsIFrame* GetNextContinuation() const override;
+
+  // Set a previous/next non-fluid continuation.
+  virtual void SetPrevContinuation(nsIFrame*) override;
+  virtual void SetNextContinuation(nsIFrame*) override;
+
+  // Get the first/last continuation for this frame.
+  virtual nsIFrame* FirstContinuation() const override;
+  virtual nsIFrame* LastContinuation() const override;
+
+#ifdef DEBUG
+  // Can aFrame2 be reached from aFrame1 by following prev/next continuations?
+  static bool IsInPrevContinuationChain(nsIFrame* aFrame1, nsIFrame* aFrame2);
+  static bool IsInNextContinuationChain(nsIFrame* aFrame1, nsIFrame* aFrame2);
+#endif
+  
+  // Get the previous/next continuation, only if it is fluid (an "in-flow").
+  nsIFrame* GetPrevInFlow() const;
+  nsIFrame* GetNextInFlow() const;
+
+  virtual nsIFrame* GetPrevInFlowVirtual() const override { return GetPrevInFlow(); }
+  virtual nsIFrame* GetNextInFlowVirtual() const override { return GetNextInFlow(); }
+  
+  // Set a previous/next fluid continuation.
+  virtual void SetPrevInFlow(nsIFrame*) override;
+  virtual void SetNextInFlow(nsIFrame*) override;
+
+  // Get the first/last frame in the current flow.
+  virtual nsIFrame* FirstInFlow() const override;
+  virtual nsIFrame* LastInFlow() const override;
+
+  // Remove the frame from the flow. Connects the frame's prev-in-flow
+  // and its next-in-flow. This should only be called in frame Destroy() methods.
+  static void RemoveFromFlow(nsIFrame* aFrame);
+
+protected:
+  explicit nsSplittableFrame(nsStyleContext* aContext) : nsFrame(aContext) {}
+
+  /**
+   * Determine the height consumed by our previous-in-flows.
+   *
+   * @note (bz) This makes laying out a splittable frame with N in-flows
+   *       O(N^2)! So, use this function with caution and minimize the number
+   *       of calls to this method.
+   */
+  nscoord GetConsumedBSize() const;
+
+  /**
+   * Retrieve the effective computed block size of this frame, which is the
+   * computed block size, minus the block size consumed by any previous in-flows.
+   */
+  nscoord GetEffectiveComputedBSize(const ReflowInput& aReflowInput,
+                                    nscoord aConsumed = NS_INTRINSICSIZE) const;
+
+  /**
+   * @see nsIFrame::GetLogicalSkipSides()
+   */
+  virtual LogicalSides GetLogicalSkipSides(const ReflowInput* aReflowInput = nullptr) const override;
+
+  /**
+   * A faster version of GetLogicalSkipSides() that is intended to be used
+   * inside Reflow before it's known if |this| frame will be COMPLETE or not.
+   * It returns a result that assumes this fragment is the last and thus
+   * should apply the block-end border/padding etc (except for "true" overflow
+   * containers which always skip block sides).  You're then expected to
+   * recalculate the block-end side (as needed) when you know |this| frame's
+   * reflow status is INCOMPLETE.
+   * This method is intended for frames that breaks in the block axis.
+   */
+  LogicalSides PreReflowBlockLevelLogicalSkipSides() const;
+
+#ifdef DEBUG
+  virtual void DumpBaseRegressionData(nsPresContext* aPresContext, FILE* out, int32_t aIndent) override;
+#endif
+
+  nsIFrame*   mPrevContinuation;
+  nsIFrame*   mNextContinuation;
+};
+
+#endif /* nsSplittableFrame_h___ */