Add infrastructure for partial layouts

Source/core/rendering/PartialLayoutState.h

+/*
+ * Copyright (C) 2013 Google Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * 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.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef PartialLayoutState_h
+#define PartialLayoutState_h
+
+#include "core/rendering/RenderObject.h"
+
+namespace WebCore {
+
+class PartialLayoutState {
+    friend class PartialLayoutDisabler;
+public:
+    PartialLayoutState()
+        : m_shouldStop(false)
+        , m_stopAtRenderer(0)
+        , m_disableCount(0)
+    {
+    }
+
+    // True if we plan to do a partial layout, or are in the process of stopping a partial layout.
+    bool isPartialLayout() const { return m_stopAtRenderer || m_shouldStop; }
+
+    bool isStopping() const { return m_shouldStop; }
+    bool checkPartialLayoutComplete(const RenderObject*);
+    void setStopAtRenderer(const RenderObject* renderer) { m_stopAtRenderer = renderer; }
+    void reset() { m_shouldStop = false; m_stopAtRenderer = 0; }
+
+private:
+    void disable() { ASSERT(!m_shouldStop); m_disableCount++; }
+    void enable() { ASSERT(m_disableCount > 0); m_disableCount--; }
+    const RenderObject* stopAtRenderer() const { return m_disableCount > 0 ? 0 : m_stopAtRenderer; }
+
+    bool m_shouldStop;
+    const RenderObject* m_stopAtRenderer;
+    int m_disableCount;
+};
+
+inline bool PartialLayoutState::checkPartialLayoutComplete(const RenderObject* renderer)
+{
+    if (m_shouldStop)
+        return true;
+
+    if (renderer == stopAtRenderer()) {
+        m_shouldStop = true;
+        m_stopAtRenderer = 0;
+        return true;
+    }
+
+    return false;
+}
+
+class PartialLayoutDisabler {
+    WTF_MAKE_NONCOPYABLE(PartialLayoutDisabler);
+public:
+    PartialLayoutDisabler(PartialLayoutState& partialLayout, bool disable = true)
+        : m_partialLayout(partialLayout)
+        , m_disable(disable)
+    {
+        if (m_disable)
+            m_partialLayout.disable();
+    }
+
+    ~PartialLayoutDisabler()
+    {
+        if (m_disable)
+            m_partialLayout.enable();
+    }
+private:
+    PartialLayoutState& m_partialLayout;
+    bool m_disable;
+};
+
+} // namespace WebCore
+
+#endif // PartialLayoutState_h