Make ScrollbarThemeAura selectively invalidate scrollbar parts.

third_party/WebKit/Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 2055 matching lines @@
         m_pendingScrollDelta += scrollDelta;
 
     clearScrollAnchor();
     updateLayersAndCompositingAfterScrollIfNeeded();
     scrollPositionChanged();
     frame().loader().client()->didChangeScrollOffset();
 }
 
 void FrameView::invalidatePaintForTickmarks()
 {
-    if (Scrollbar* scrollbar = verticalScrollbar()) {
-        scrollbar->setTrackNeedsRepaint(true);
-        setScrollbarNeedsPaintInvalidation(VerticalScrollbar);
-    }
+    if (Scrollbar* scrollbar = verticalScrollbar())
+        scrollbar->setNeedsPaintInvalidation(static_cast<ScrollbarPart>(~ThumbPart));

[skobes, 2015/12/28 17:48:39]

Why do we exclude ThumbPart here?

[jbroman, 2015/12/29 16:45:14]

The previous version of the code invalidates the track, but not the thumb. (From
cc's perspective, the scrollbar consists of a track quad and a thumb quad.)
There are a variety of scrollbar parts that all end up in the track quad (and
it's not important to specify which of these draws the tickmarks), but I'd like
not to invalidate the thumb here, since the existing code doesn't.

If you'd rather also invalidate the thumb, I can do that.

 }
 
 void FrameView::getTickmarks(Vector<IntRect>& tickmarks) const
 {
     if (!m_tickmarks.isEmpty())
         tickmarks = m_tickmarks;
     else
         tickmarks = frame().document()->markers().renderedRectsForMarkers(DocumentMarker::TextMatch);
 }
 
@@ skipping 1918 matching lines @@
     return m_hiddenForThrottling && m_crossOriginForThrottling;
 }
 
 LayoutBox& FrameView::boxForScrollControlPaintInvalidation() const
 {
     ASSERT(layoutView());
     return *layoutView();
 }
 
 } // namespace blink