Make ScrollbarThemeAura selectively invalidate scrollbar parts.

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

Index: third_party/WebKit/Source/core/frame/FrameView.cpp
diff --git a/third_party/WebKit/Source/core/frame/FrameView.cpp b/third_party/WebKit/Source/core/frame/FrameView.cpp
index de49f4bed8fe9b65c1d2548956bca675c16783dc..c5895a27e3ce2667073262e178f3d88b78521ed9 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.cpp
+++ b/third_party/WebKit/Source/core/frame/FrameView.cpp
@@ -2073,10 +2073,8 @@ void FrameView::scrollTo(const DoublePoint& newPosition)
 
 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