color_utils cleanup:

mash/wm/frame/default_header_painter.cc

Index: mash/wm/frame/default_header_painter.cc
diff --git a/mash/wm/frame/default_header_painter.cc b/mash/wm/frame/default_header_painter.cc
index ed2a66d1be487064279a10fe23211ba1df21bee2..dfc1ed14cef749860eb87cefa09f47ccfe046b2b 100644
--- a/mash/wm/frame/default_header_painter.cc
+++ b/mash/wm/frame/default_header_painter.cc
@@ -40,8 +40,6 @@ const SkColor kHeaderContentSeparatorInactiveColor =
 const SkColor kDefaultFrameColor = SkColorSetRGB(242, 242, 242);
 // Duration of crossfade animation for activating and deactivating frame.
 const int kActivationCrossfadeDurationMs = 200;
-// Luminance below which to use white caption buttons.
-const int kMaxLuminanceForLightButtons = 125;
 
 // Tiles an image into an area, rounding the top corners.
 void TileRoundRect(gfx::Canvas* canvas,
@@ -269,9 +267,8 @@ void DefaultHeaderPainter::PaintHeaderContentSeparator(gfx::Canvas* canvas) {
 }
 
 bool DefaultHeaderPainter::ShouldUseLightImages() {
-  int luminance = color_utils::GetLuminanceForColor(
+  return color_utils::IsDark(
       mode_ == MODE_INACTIVE ? inactive_frame_color_ : active_frame_color_);
-  return luminance < kMaxLuminanceForLightButtons;
 }
 
 void DefaultHeaderPainter::UpdateAllButtonImages() {