Mac: Don't repaint scrollbars every frame

cc/test/fake_scrollbar.cc

Index: cc/test/fake_scrollbar.cc
diff --git a/cc/test/fake_scrollbar.cc b/cc/test/fake_scrollbar.cc
index 754b6f75997901aad3491a5ef29dc80cdfaa6f4e..80bd44422a301c8fcb595ce64d2b664ad12c20b9 100644
--- a/cc/test/fake_scrollbar.cc
+++ b/cc/test/fake_scrollbar.cc
@@ -15,6 +15,9 @@ FakeScrollbar::FakeScrollbar()
       is_overlay_(false),
       thumb_thickness_(10),
       thumb_length_(5),
+      thumb_opacity_(1),
+      needs_paint_thumb_(true),
+      needs_paint_track_(true),
       track_rect_(0, 0, 100, 10),
       fill_color_(SK_ColorGREEN) {}
 
@@ -24,6 +27,9 @@ FakeScrollbar::FakeScrollbar(bool paint, bool has_thumb, bool is_overlay)
       is_overlay_(is_overlay),
       thumb_thickness_(10),
       thumb_length_(5),
+      thumb_opacity_(1),
+      needs_paint_thumb_(true),
+      needs_paint_track_(true),
       track_rect_(0, 0, 100, 10),
       fill_color_(SK_ColorGREEN) {}
 
@@ -55,6 +61,16 @@ gfx::Rect FakeScrollbar::TrackRect() const {
   return track_rect_;
 }
 
+float FakeScrollbar::ThumbOpacity() const {
+  return thumb_opacity_;
+}
+
+bool FakeScrollbar::NeedsPaintPart(ScrollbarPart part) const {
+  if (part == THUMB)
+    return needs_paint_thumb_;
+  return needs_paint_track_;
+}
+
 void FakeScrollbar::PaintPart(SkCanvas* canvas,
                              ScrollbarPart part,
                              const gfx::Rect& content_rect) {