Make ScrollbarThemeAura selectively invalidate scrollbar parts.

third_party/WebKit/Source/platform/scroll/Scrollbar.cpp

 /*
  * Copyright (C) 2004, 2006, 2008 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 108 matching lines @@
     return m_scrollableArea && m_scrollableArea->isActive();
 }
 
 bool Scrollbar::isLeftSideVerticalScrollbar() const
 {
     if (m_orientation == VerticalScrollbar && m_scrollableArea)
         return m_scrollableArea->shouldPlaceVerticalScrollbarOnLeft();
     return false;
 }
 
-void Scrollbar::offsetDidChange()
+bool Scrollbar::offsetDidChange()
 {
     ASSERT(m_scrollableArea);
 
     float position = scrollableAreaCurrentPos();
     if (position == m_currentPos)
-        return;
+        return false;
 
+    float oldPosition = m_currentPos;
     int oldThumbPosition = theme().thumbPosition(*this);
     m_currentPos = position;
-    updateThumbPosition();
+
+    ScrollbarPart invalidParts = theme().invalidateOnThumbPositionChange(
+        *this, oldPosition, position);
+    if (invalidParts != NoPart)
+        setNeedsPaintInvalidation(invalidParts);
+
     if (m_pressedPart == ThumbPart)
         setPressedPos(m_pressedPos + theme().thumbPosition(*this) - oldThumbPosition);
+
+    return true;
 }
 
 void Scrollbar::disconnectFromScrollableArea()
 {
     m_scrollableArea = nullptr;
 }
 
 void Scrollbar::setProportion(int visibleSize, int totalSize)
 {
     if (visibleSize == m_visibleSize && totalSize == m_totalSize)
         return;
 
     m_visibleSize = visibleSize;
     m_totalSize = totalSize;
 
-    updateThumbProportion();
-}
-
-void Scrollbar::updateThumb()
-{
     setNeedsPaintInvalidation();
 }
 
-void Scrollbar::updateThumbPosition()
-{
-    updateThumb();
-}
-
-void Scrollbar::updateThumbProportion()
-{
-    updateThumb();
-}
-
 void Scrollbar::paint(GraphicsContext& context, const CullRect& cullRect) const
 {
     if (!cullRect.intersectsCullRect(frameRect()))
         return;
 
     if (!theme().paint(*this, context, cullRect))
         Widget::paint(context, cullRect);
 }
 
 void Scrollbar::autoscrollTimerFired(Timer<Scrollbar>*)
@@ skipping 125 matching lines @@
 }
 
 void Scrollbar::setHoveredPart(ScrollbarPart part)
 {
     if (part == m_hoveredPart)
         return;
 
     if (((m_hoveredPart == NoPart || part == NoPart) && theme().invalidateOnMouseEnterExit())
         // When there's a pressed part, we don't draw a hovered state, so there's no reason to invalidate.
         || m_pressedPart == NoPart)
-        setNeedsPaintInvalidation();
+        setNeedsPaintInvalidation(static_cast<ScrollbarPart>(m_hoveredPart | part));
 
     m_hoveredPart = part;
 }
 
 void Scrollbar::setPressedPart(ScrollbarPart part)
 {
     if (m_pressedPart != NoPart
         // When we no longer have a pressed part, we can start drawing a hovered state on the hovered part.
         || m_hoveredPart != NoPart)
-        setNeedsPaintInvalidation();
+        setNeedsPaintInvalidation(static_cast<ScrollbarPart>(m_pressedPart | m_hoveredPart | part));
     m_pressedPart = part;
 }
 
 bool Scrollbar::gestureEvent(const PlatformGestureEvent& evt)
 {
     switch (evt.type()) {
     case PlatformEvent::GestureTapDown:
         setPressedPart(theme().hitTest(*this, evt.position()));
         m_pressedPos = orientation() == HorizontalScrollbar ? convertFromRootFrame(evt.position()).x() : convertFromRootFrame(evt.position()).y();
         return true;
@@ skipping 214 matching lines @@
 {
     if (!m_scrollableArea)
         return 0;
 
     if (m_orientation == HorizontalScrollbar)
         return m_scrollableArea->scrollPosition().x() - m_scrollableArea->minimumScrollPosition().x();
 
     return m_scrollableArea->scrollPosition().y() - m_scrollableArea->minimumScrollPosition().y();
 }
 
-void Scrollbar::setNeedsPaintInvalidation()
+void Scrollbar::setNeedsPaintInvalidation(ScrollbarPart parts)
 {
-    if (m_theme.shouldRepaintAllPartsOnInvalidation()) {
+    if (m_theme.shouldRepaintAllPartsOnInvalidation())
+        parts = AllParts;
+    if (parts & ~ThumbPart)
         m_trackNeedsRepaint = true;
+    if (parts & ThumbPart)
         m_thumbNeedsRepaint = true;
-    }
     if (m_scrollableArea)
         m_scrollableArea->setScrollbarNeedsPaintInvalidation(orientation());
 }
 
 } // namespace blink