diff -r 000000000000 -r 6474c204b198 layout/style/nsRuleWalker.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/layout/style/nsRuleWalker.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,105 @@
+/* -*- 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/. */
+
+/*
+ * a class that walks the lexicographic tree of rule nodes as style
+ * rules are matched
+ */
+
+#ifndef nsRuleWalker_h_
+#define nsRuleWalker_h_
+
+#include "nsRuleNode.h"
+#include "nsIStyleRule.h"
+#include "StyleRule.h"
+
+class nsRuleWalker {
+public:
+  nsRuleNode* CurrentNode() { return mCurrent; }
+  void SetCurrentNode(nsRuleNode* aNode) {
+    NS_ASSERTION(aNode, "Must have node here!");
+    mCurrent = aNode;
+  }
+
+protected:
+  void DoForward(nsIStyleRule* aRule) {
+    mCurrent = mCurrent->Transition(aRule, mLevel, mImportance);
+    NS_POSTCONDITION(mCurrent, "Transition messed up");
+  }
+
+public:
+  void Forward(nsIStyleRule* aRule) {
+    NS_PRECONDITION(!nsRefPtr<mozilla::css::StyleRule>(do_QueryObject(aRule)),
+                    "Calling the wrong Forward() overload");
+    DoForward(aRule);
+  }
+  void Forward(mozilla::css::StyleRule* aRule) {
+    DoForward(aRule);
+    mCheckForImportantRules =
+      mCheckForImportantRules && !aRule->GetImportantRule();
+  }
+  // ForwardOnPossiblyCSSRule should only be used by callers that have
+  // an explicit list of rules they need to walk, with the list
+  // already containing any important rules they care about.
+  void ForwardOnPossiblyCSSRule(nsIStyleRule* aRule) {
+    DoForward(aRule);
+  }
+
+  void Reset() { mCurrent = mRoot; }
+
+  bool AtRoot() { return mCurrent == mRoot; }
+
+  void SetLevel(uint8_t aLevel, bool aImportance,
+                bool aCheckForImportantRules) {
+    NS_ASSERTION(!aCheckForImportantRules || !aImportance,
+                 "Shouldn't be checking for important rules while walking "
+                 "important rules");
+    mLevel = aLevel;
+    mImportance = aImportance;
+    mCheckForImportantRules = aCheckForImportantRules;
+  }
+  uint8_t GetLevel() const { return mLevel; }
+  bool GetImportance() const { return mImportance; }
+  bool GetCheckForImportantRules() const { return mCheckForImportantRules; }
+
+  bool AuthorStyleDisabled() const { return mAuthorStyleDisabled; }
+
+  // We define the visited-relevant link to be the link that is the
+  // nearest self-or-ancestor to the node being matched.
+  enum VisitedHandlingType {
+    // Do rule matching as though all links are unvisited.
+    eRelevantLinkUnvisited,
+    // Do rule matching as though the relevant link is visited and all
+    // other links are unvisited.
+    eRelevantLinkVisited,
+    // Do rule matching as though a rule should match if it would match
+    // given any set of visitedness states.  (used by users other than
+    // nsRuleWalker)
+    eLinksVisitedOrUnvisited
+  };
+
+private:
+  nsRuleNode* mCurrent; // Our current position.  Never null.
+  nsRuleNode* mRoot; // The root of the tree we're walking.
+  uint8_t mLevel; // an nsStyleSet::sheetType
+  bool mImportance;
+  bool mCheckForImportantRules; // If true, check for important rules as
+                                // we walk and set to false if we find
+                                // one.
+  bool mAuthorStyleDisabled;
+
+public:
+  nsRuleWalker(nsRuleNode* aRoot, bool aAuthorStyleDisabled)
+    : mCurrent(aRoot)
+    , mRoot(aRoot)
+    , mAuthorStyleDisabled(aAuthorStyleDisabled)
+  {
+    NS_ASSERTION(mCurrent, "Caller screwed up and gave us null node");
+    MOZ_COUNT_CTOR(nsRuleWalker);
+  }
+  ~nsRuleWalker() { MOZ_COUNT_DTOR(nsRuleWalker); }
+};
+
+#endif /* !defined(nsRuleWalker_h_) */