Factor the style invalidation tree walk out of RuleFeatureSet, and make it generic.

Source/core/css/invalidation/StyleInvalidator.h

Index: Source/core/css/invalidation/StyleInvalidator.h
diff --git a/Source/core/css/invalidation/StyleInvalidator.h b/Source/core/css/invalidation/StyleInvalidator.h
new file mode 100644
index 0000000000000000000000000000000000000000..ce670cb79492f055f06f820a379cc7362e544f5b
--- /dev/null
+++ b/Source/core/css/invalidation/StyleInvalidator.h
@@ -0,0 +1,61 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef StyleInvalidator_h
+#define StyleInvalidator_h
+
+#include "core/css/RuleFeature.h"
+#include "heap/Heap.h"
+
+namespace WebCore {
+
+class StyleInvalidator {
+    STACK_ALLOCATED();
+public:
+    explicit StyleInvalidator(Document&);
+    void invalidate();
+
+private:
+    bool invalidate(Element&);
+    bool invalidateChildren(Element&);
+
+    bool checkInvalidationSetsAgainstElement(Element&);
+
+    struct RecursionData {
+        RecursionData() : m_foundInvalidationSet(false) { }
+        void pushInvalidationSet(const DescendantInvalidationSet&);
+        bool matchesCurrentInvalidationSets(Element&);
+        bool foundInvalidationSet() { return m_foundInvalidationSet; }
+
+        Vector<AtomicString> m_invalidationClasses;
+        bool m_foundInvalidationSet;
+    };
+
+    class RecursionCheckpoint {
+    public:
+        RecursionCheckpoint(RecursionData* data)
+            : m_prevClassLength(data->m_invalidationClasses.size()),
+            m_prevFoundInvalidationSet(data->m_foundInvalidationSet),
+            m_data(data)
+        { }
+        ~RecursionCheckpoint()
+        {
+            m_data->m_invalidationClasses.remove(m_prevClassLength, m_data->m_invalidationClasses.size() - m_prevClassLength);
+            m_data->m_foundInvalidationSet = m_prevFoundInvalidationSet;
+        }
+
+    private:
+        int m_prevClassLength;
+        bool m_prevFoundInvalidationSet;
+        RecursionData* m_data;
+    };
+
+    Document& m_document;
+    RuleFeatureSet::PendingInvalidationMap& m_pendingInvalidationMap;
+    RecursionData m_recursionData;
+};
+
+} // namespace WebCore
+
+#endif // StyleInvalidator_h