diff -r 000000000000 -r 6474c204b198 layout/xul/tree/nsTreeStyleCache.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/layout/xul/tree/nsTreeStyleCache.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,111 @@
+/* -*- 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 nsTreeStyleCache_h__
+#define nsTreeStyleCache_h__
+
+#include "mozilla/Attributes.h"
+#include "nsHashtable.h"
+#include "nsIAtom.h"
+#include "nsCOMArray.h"
+#include "nsICSSPseudoComparator.h"
+#include "nsStyleContext.h"
+
+typedef nsCOMArray<nsIAtom> AtomArray;
+
+class nsDFAState : public nsHashKey
+{
+public:
+  uint32_t mStateID;
+
+  nsDFAState(uint32_t aID) :mStateID(aID) {}
+
+  uint32_t GetStateID() { return mStateID; }
+
+  uint32_t HashCode(void) const MOZ_OVERRIDE {
+    return mStateID;
+  }
+
+  bool Equals(const nsHashKey *aKey) const MOZ_OVERRIDE {
+    nsDFAState* key = (nsDFAState*)aKey;
+    return key->mStateID == mStateID;
+  }
+
+  nsHashKey *Clone(void) const MOZ_OVERRIDE {
+    return new nsDFAState(mStateID);
+  }
+};
+
+class nsTransitionKey : public nsHashKey
+{
+public:
+  uint32_t mState;
+  nsCOMPtr<nsIAtom> mInputSymbol;
+
+  nsTransitionKey(uint32_t aState, nsIAtom* aSymbol) :mState(aState), mInputSymbol(aSymbol) {}
+
+  uint32_t HashCode(void) const MOZ_OVERRIDE {
+    // Make a 32-bit integer that combines the low-order 16 bits of the state and the input symbol.
+    int32_t hb = mState << 16;
+    int32_t lb = (NS_PTR_TO_INT32(mInputSymbol.get()) << 16) >> 16;
+    return hb+lb;
+  }
+
+  bool Equals(const nsHashKey *aKey) const MOZ_OVERRIDE {
+    nsTransitionKey* key = (nsTransitionKey*)aKey;
+    return key->mState == mState && key->mInputSymbol == mInputSymbol;
+  }
+
+  nsHashKey *Clone(void) const MOZ_OVERRIDE {
+    return new nsTransitionKey(mState, mInputSymbol);
+  }
+};
+
+class nsTreeStyleCache 
+{
+public:
+  nsTreeStyleCache() :mTransitionTable(nullptr), mCache(nullptr), mNextState(0) {}
+  ~nsTreeStyleCache() { Clear(); }
+
+  void Clear() { delete mTransitionTable; mTransitionTable = nullptr; delete mCache; mCache = nullptr; mNextState = 0; }
+
+  nsStyleContext* GetStyleContext(nsICSSPseudoComparator* aComparator,
+                                  nsPresContext* aPresContext, 
+                                  nsIContent* aContent, 
+                                  nsStyleContext* aContext,
+                                  nsIAtom* aPseudoElement,
+                                  const AtomArray & aInputWord);
+
+  static bool DeleteDFAState(nsHashKey *aKey, void *aData, void *closure);
+
+  static bool ReleaseStyleContext(nsHashKey *aKey, void *aData, void *closure);
+
+protected:
+  // A transition table for a deterministic finite automaton.  The DFA
+  // takes as its input a single pseudoelement and an ordered set of properties.  
+  // It transitions on an input word that is the concatenation of the pseudoelement supplied
+  // with the properties in the array.
+  // 
+  // It transitions from state to state by looking up entries in the transition table (which is
+  // a mapping from (S,i)->S', where S is the current state, i is the next
+  // property in the input word, and S' is the state to transition to.
+  //
+  // If S' is not found, it is constructed and entered into the hashtable
+  // under the key (S,i).
+  //
+  // Once the entire word has been consumed, the final state is used
+  // to reference the cache table to locate the style context.
+  nsObjectHashtable* mTransitionTable;
+
+  // The cache of all active style contexts.  This is a hash from 
+  // a final state in the DFA, Sf, to the resultant style context.
+  nsObjectHashtable* mCache;
+
+  // An integer counter that is used when we need to make new states in the
+  // DFA.
+  uint32_t mNextState;
+};
+
+#endif // nsTreeStyleCache_h__