Reverse style resolution to avoid N^2 walk when building the render tree

Source/core/dom/WhitespaceChildList.h

Index: Source/core/dom/WhitespaceChildList.h
diff --git a/Source/core/platform/Task.h b/Source/core/dom/WhitespaceChildList.h
similarity index 56%
copy from Source/core/platform/Task.h
copy to Source/core/dom/WhitespaceChildList.h
index b9d2e46802aebf6391df4ec3dabb580d43b2483c..b5a4fb14f656e6ca69c20b1dbf92c26bc71b2b9b 100644
--- a/Source/core/platform/Task.h
+++ b/Source/core/dom/WhitespaceChildList.h
@@ -7,10 +7,6 @@
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
- *     * Redistributions in binary form must reproduce the above
- * copyright notice, this list of conditions and the following disclaimer
- * in the documentation and/or other materials provided with the
- * distribution.
  *     * Neither the name of Google Inc. nor the names of its
  * contributors may be used to endorse or promote products derived from
  * this software without specific prior written permission.
@@ -28,30 +24,48 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef Task_h
-#define Task_h
+#ifndef WhitespaceChildList_h
+#define WhitespaceChildList_h
 
-#include "wtf/Functional.h"
-#include "public/platform/WebThread.h"
+#include "core/dom/Text.h"
+#include "core/rendering/style/RenderStyleConstants.h"
 
 namespace WebCore {
 
-class Task : public WebKit::WebThread::Task {
+class Text;
+
+// Tracks a limited number of whitespace text children during style recalc
+// to postpone their style recalc as part of optimization to avoid creating
+// unnecessary whitespace text renderers. If we hit the limit, it recalcs
+// the whitespace text's style and clears the list.
+class WhitespaceChildList {
 public:
-    explicit Task(const Closure& closure)
-        : m_closure(closure)
+    WhitespaceChildList(StyleRecalcChange change)
+        : m_change(change)
+    { }
+
+    void append(Text* textChild)
     {
+        ASSERT(textChild->containsOnlyWhitespace());
+        if (m_list.size() == maxWhitespaceChildrenToDefer) {
+            recalcStyle();
+            m_list.clear();
+        }
+        m_list.append(textChild);
     }
 
-    virtual void run() OVERRIDE
+    void recalcStyle() const
     {
-        m_closure();
+        for (unsigned i = 0; i < m_list.size(); ++i)
+            m_list[i]->recalcTextStyle(m_change);
     }
-
 private:
-    Closure m_closure;
+    StyleRecalcChange m_change;
+
+    static const unsigned maxWhitespaceChildrenToDefer = 10;
+    Vector<Text*, maxWhitespaceChildrenToDefer> m_list;
 };
 
 } // namespace WebCore
 
-#endif // Task_h
+#endif // WhitespaceChildList_h