Mac: Don't repaint scrollbars every frame

cc/test/fake_scrollbar.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/test/fake_scrollbar.h"
 
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "ui/gfx/skia_util.h"
 
 namespace cc {
 
 FakeScrollbar::FakeScrollbar()
     : paint_(false),
       has_thumb_(false),
       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) {}
 
 FakeScrollbar::FakeScrollbar(bool paint, bool has_thumb, bool is_overlay)
     : paint_(paint),
       has_thumb_(has_thumb),
       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) {}
 
 FakeScrollbar::~FakeScrollbar() {}
 
 ScrollbarOrientation FakeScrollbar::Orientation() const {
   return HORIZONTAL;
 }
 
 bool FakeScrollbar::IsLeftSideVerticalScrollbar() const {
@@ skipping 11 matching lines @@
 }
 
 int FakeScrollbar::ThumbLength() const {
   return thumb_length_;
 }
 
 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) {
   if (!paint_)
     return;
 
   // Fill the scrollbar with a different color each time.
   fill_color_++;
   SkPaint paint;
   paint.setAntiAlias(false);
   paint.setColor(paint_fill_color());
   paint.setStyle(SkPaint::kFill_Style);
 
   // Emulate the how the real scrollbar works by using scrollbar's rect for
   // TRACK and the given content_rect for the THUMB
   SkRect rect = part == TRACK ? RectToSkRect(TrackRect())
                               : RectToSkRect(content_rect);
   canvas->drawRect(rect, paint);
 }
 
 }  // namespace cc