Mac: Don't repaint scrollbars every frame

third_party/WebKit/public/platform/WebScrollbarThemePainter.h

Index: third_party/WebKit/public/platform/WebScrollbarThemePainter.h
diff --git a/third_party/WebKit/public/platform/WebScrollbarThemePainter.h b/third_party/WebKit/public/platform/WebScrollbarThemePainter.h
index 6563a6e65b533381525d75d541d02ed2601eef06..fcbfe14b7d9bffda9581d9c0ebce630bbd224061 100644
--- a/third_party/WebKit/public/platform/WebScrollbarThemePainter.h
+++ b/third_party/WebKit/public/platform/WebScrollbarThemePainter.h
@@ -64,6 +64,12 @@ public:
     BLINK_PLATFORM_EXPORT void paintTickmarks(WebCanvas*, const WebRect&);
     BLINK_PLATFORM_EXPORT void paintThumb(WebCanvas*, const WebRect&);
 
+    // This opacity is applied on top of the content that is painted for the thumb.
+    BLINK_PLATFORM_EXPORT float thumbOpacity() const;
+
+    BLINK_PLATFORM_EXPORT bool trackNeedsRepaint() const;
+    BLINK_PLATFORM_EXPORT bool thumbNeedsRepaint() const;
+
 #if INSIDE_BLINK
     BLINK_PLATFORM_EXPORT WebScrollbarThemePainter(ScrollbarTheme*, Scrollbar*, float deviceScaleFactor);
 #endif