Calculate paint invalidation rect for scrollbars

third_party/WebKit/Source/core/paint/PaintInvalidationCapableScrollableArea.h

Index: third_party/WebKit/Source/core/paint/PaintInvalidationCapableScrollableArea.h
diff --git a/third_party/WebKit/Source/core/paint/PaintInvalidationCapableScrollableArea.h b/third_party/WebKit/Source/core/paint/PaintInvalidationCapableScrollableArea.h
new file mode 100644
index 0000000000000000000000000000000000000000..4fbe1ab14a50aeca0991678d70f35dbb41ab03e4
--- /dev/null
+++ b/third_party/WebKit/Source/core/paint/PaintInvalidationCapableScrollableArea.h
@@ -0,0 +1,40 @@
+// Copyright 2015 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 PaintInvalidationCapableScrollableArea_h
+#define PaintInvalidationCapableScrollableArea_h
+
+#include "core/CoreExport.h"
+#include "platform/geometry/LayoutRect.h"
+#include "platform/scroll/ScrollableArea.h"
+
+namespace blink {
+
+class LayoutBox;
+class LayoutBoxModelObject;
+class LayoutScrollbarPart;
+class PaintInvalidationContainer;
+class PaintInvalidationState;
+
+// Base class of FrameView and PaintLayerScrollableArea to share paint invalidation code.
+// TODO(wangxianzhu): Combine this into PaintLayerScrollableArea when FrameView no longer scrolls.
+class CORE_EXPORT PaintInvalidationCapableScrollableArea : public ScrollableArea {
+public:
+    // The LayoutBox parameter is the LayoutView of a FrameView if the scrollbars belong to the FrameView,
+    // or the box() of a PaintLayerScrollbarArea if the scrollbars belong to the PaintLayerScrollableArea.
+    void willRemoveScrollbar(LayoutBox&, Scrollbar*, ScrollbarOrientation);
+
+    void invalidatePaintOfScrollControlsIfNeeded(LayoutBox& ownerBox, const PaintInvalidationState&, const LayoutBoxModelObject& paintInvalidationContainer, LayoutScrollbarPart* scrollCorner, LayoutScrollbarPart* resizer);
+
+private:
+    void willRemoveScrollbar(Scrollbar*, ScrollbarOrientation) override { ASSERT_NOT_REACHED(); }
+
+    LayoutRect m_horizontalScrollbarPreviousPaintInvalidationRect;
+    LayoutRect m_verticalScrollbarPreviousPaintInvalidationRect;
+    LayoutRect m_scrollCornerPreviousPaintInvalidationRect;
+};
+
+} // namespace blink
+
+#endif // PaintInvalidationCapableScrollableArea_h