MacViews: Overlay Scrollbars with Show/Hide Animations

ui/native_theme/native_theme_mac.mm

Index: ui/native_theme/native_theme_mac.mm
diff --git a/ui/native_theme/native_theme_mac.mm b/ui/native_theme/native_theme_mac.mm
index 43eb1296316e424026f8bee6f435ea1696b25d8e..dfda092d948c8f252e50951a938d98b2d6f520d8 100644
--- a/ui/native_theme/native_theme_mac.mm
+++ b/ui/native_theme/native_theme_mac.mm
@@ -122,6 +122,14 @@ SkColor NSSystemColorToSkColor(NSColor* color) {
                         SkScalarRoundToInt(255.0 * components[0]));
 }
 
+SkColor GetColorFromOverlayParams(
+    SkColor color,
+    ui::NativeTheme::OverlayParams overlay_params) {
+  return overlay_params.is_overlay
+             ? SkColorSetA(color, SkColorGetA(color) * overlay_params.alpha)
+             : color;
+}
+
 }  // namespace
 
 namespace ui {
@@ -256,6 +264,8 @@ void NativeThemeMac::PaintScrollbarTrack(
     gradient_bounds[0].set(rect.x(), rect.y());
     gradient_bounds[1].set(rect.x(), rect.bottom());
   }
+
+  // TODO(spqchan): Change the opacity of the track when it's overlayed.
   skia::RefPtr<SkShader> shader = skia::AdoptRef(
       SkGradientShader::CreateLinear(gradient_bounds,
                                      kScrollerTrackGradientColors,
@@ -271,13 +281,15 @@ void NativeThemeMac::PaintScrollbarTrack(
   // Draw inner and outer line borders.
   if (part == kScrollbarVerticalTrack) {
     SkPaint paint;
-    paint.setColor(kScrollerTrackInnerBorderColor);
+    paint.setColor(GetColorFromOverlayParams(kScrollerTrackInnerBorderColor,
+                                             extra_params.overlay));
     canvas->drawRectCoords(track_rect.left(),
                            track_rect.top(),
                            track_rect.left() + kScrollerTrackBorderWidth,
                            track_rect.bottom(),
                            paint);
-    paint.setColor(kScrollerTrackOuterBorderColor);
+    paint.setColor(GetColorFromOverlayParams(kScrollerTrackOuterBorderColor,
+                                             extra_params.overlay));
     canvas->drawRectCoords(track_rect.right() - kScrollerTrackBorderWidth,
                            track_rect.top(),
                            track_rect.right(),
@@ -285,13 +297,15 @@ void NativeThemeMac::PaintScrollbarTrack(
                            paint);
   } else {
     SkPaint paint;
-    paint.setColor(kScrollerTrackInnerBorderColor);
+    paint.setColor(GetColorFromOverlayParams(kScrollerTrackInnerBorderColor,
+                                             extra_params.overlay));
     canvas->drawRectCoords(track_rect.left(),
                            track_rect.top(),
                            track_rect.right(),
                            track_rect.top() + kScrollerTrackBorderWidth,
                            paint);
-    paint.setColor(kScrollerTrackOuterBorderColor);
+    paint.setColor(GetColorFromOverlayParams(kScrollerTrackOuterBorderColor,
+                                             extra_params.overlay));
     canvas->drawRectCoords(track_rect.left(),
                            track_rect.bottom() - kScrollerTrackBorderWidth,
                            track_rect.right(),
@@ -300,10 +314,12 @@ void NativeThemeMac::PaintScrollbarTrack(
   }
 }
 
-void NativeThemeMac::PaintScrollbarThumb(SkCanvas* canvas,
-                                         Part part,
-                                         State state,
-                                         const gfx::Rect& rect) const {
+void NativeThemeMac::PaintScrollbarThumb(
+    SkCanvas* canvas,
+    Part part,
+    State state,
+    const ScrollbarThumbExtraParams& extra_params,
+    const gfx::Rect& rect) const {
   gfx::Rect thumb_rect(rect);
   switch (part) {
     case kScrollbarHorizontalThumb:
@@ -321,8 +337,11 @@ void NativeThemeMac::PaintScrollbarThumb(SkCanvas* canvas,
 
   SkPaint paint;
   paint.setAntiAlias(true);
-  paint.setColor(state == kHovered ? thumb_active_color_
-                                   : thumb_inactive_color_);
+
+  SkColor thumb_color =
+      state == kHovered ? thumb_active_color_ : thumb_inactive_color_;
+  paint.setColor(GetColorFromOverlayParams(thumb_color, extra_params.overlay));
+
   const SkScalar radius = std::min(rect.width(), rect.height());
   canvas->drawRoundRect(gfx::RectToSkRect(thumb_rect), radius, radius, paint);
 }