diff -r 000000000000 -r 6474c204b198 layout/style/nsCSSPropertySet.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/layout/style/nsCSSPropertySet.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,93 @@
+/* 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/. */
+
+/* bit vectors for sets of CSS properties */
+
+#ifndef nsCSSPropertySet_h__
+#define nsCSSPropertySet_h__
+
+#include "mozilla/ArrayUtils.h"
+
+#include "nsCSSProperty.h"
+#include <limits.h> // for CHAR_BIT
+
+/**
+ * nsCSSPropertySet maintains a set of non-shorthand CSS properties.  In
+ * other words, for each longhand CSS property we support, it has a bit
+ * for whether that property is in the set.
+ */
+class nsCSSPropertySet {
+public:
+    nsCSSPropertySet() { Empty(); }
+    // auto-generated copy-constructor OK
+
+    void AssertInSetRange(nsCSSProperty aProperty) const {
+        NS_ASSERTION(0 <= aProperty &&
+                     aProperty < eCSSProperty_COUNT_no_shorthands,
+                     "out of bounds");
+    }
+
+    // Conversion of aProperty to |size_t| after AssertInSetRange
+    // lets the compiler generate significantly tighter code.
+
+    void AddProperty(nsCSSProperty aProperty) {
+        AssertInSetRange(aProperty);
+        size_t p = aProperty;
+        mProperties[p / kBitsInChunk] |=
+          property_set_type(1) << (p % kBitsInChunk);
+    }
+
+    void RemoveProperty(nsCSSProperty aProperty) {
+        AssertInSetRange(aProperty);
+        size_t p = aProperty;
+        mProperties[p / kBitsInChunk] &=
+            ~(property_set_type(1) << (p % kBitsInChunk));
+    }
+
+    bool HasProperty(nsCSSProperty aProperty) const {
+        AssertInSetRange(aProperty);
+        size_t p = aProperty;
+        return (mProperties[p / kBitsInChunk] &
+                (property_set_type(1) << (p % kBitsInChunk))) != 0;
+    }
+
+    void Empty() {
+        memset(mProperties, 0, sizeof(mProperties));
+    }
+
+    void AssertIsEmpty(const char* aText) const {
+        for (size_t i = 0; i < mozilla::ArrayLength(mProperties); ++i) {
+            NS_ASSERTION(mProperties[i] == 0, aText);
+        }
+    }
+
+private:
+    typedef unsigned long property_set_type;
+public:
+    // number of bits in |property_set_type|.
+    static const size_t kBitsInChunk = sizeof(property_set_type)*CHAR_BIT;
+    // number of |property_set_type|s in the set
+    static const size_t kChunkCount =
+        (eCSSProperty_COUNT_no_shorthands + kBitsInChunk - 1) / kBitsInChunk;
+
+    /*
+     * For fast enumeration of all the bits that are set, callers can
+     * check each chunk against zero (since in normal cases few bits are
+     * likely to be set).
+     */
+    bool HasPropertyInChunk(size_t aChunk) const {
+        return mProperties[aChunk] != 0;
+    }
+    bool HasPropertyAt(size_t aChunk, size_t aBit) const {
+        return (mProperties[aChunk] & (property_set_type(1) << aBit)) != 0;
+    }
+    static nsCSSProperty CSSPropertyAt(size_t aChunk, size_t aBit) {
+        return nsCSSProperty(aChunk * kBitsInChunk + aBit);
+    }
+
+private:
+    property_set_type mProperties[kChunkCount];
+};
+
+#endif /* !defined(nsCSSPropertySet_h__) */