Mac: Don't repaint scrollbars every frame

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

Index: third_party/WebKit/Source/platform/scroll/Scrollbar.cpp
diff --git a/third_party/WebKit/Source/platform/scroll/Scrollbar.cpp b/third_party/WebKit/Source/platform/scroll/Scrollbar.cpp
index 19538b25345adfea775bd2084f30f5c464d38b67..f9a99006e8abe3505bfd37cdd845e094ca1837a0 100644
--- a/third_party/WebKit/Source/platform/scroll/Scrollbar.cpp
+++ b/third_party/WebKit/Source/platform/scroll/Scrollbar.cpp
@@ -61,6 +61,8 @@ Scrollbar::Scrollbar(ScrollableArea* scrollableArea, ScrollbarOrientation orient
     , m_overlapsResizer(false)
     , m_isAlphaLocked(false)
     , m_elasticOverscroll(0)
+    , m_trackBackgroudNeedsRepaint(true)
+    , m_thumbNeedsRepaint(true)
 {
     if (!m_theme)
         m_theme = ScrollbarTheme::theme();
@@ -541,6 +543,10 @@ float Scrollbar::scrollableAreaCurrentPos() const
 
 void Scrollbar::setNeedsPaintInvalidation()
 {
+    if (m_theme->shouldRepaintAllPartsOnInvalidation()) {
+        m_trackBackgroudNeedsRepaint = true;
+        m_thumbNeedsRepaint = true;
+    }
     if (m_scrollableArea)
         m_scrollableArea->setScrollbarNeedsPaintInvalidation(this);
 }