cros: Remove some OS platform ifdefs from ash

ash/wm/screen_dimmer_unittest.cc

Index: ash/wm/screen_dimmer_unittest.cc
diff --git a/ash/wm/screen_dimmer_unittest.cc b/ash/wm/screen_dimmer_unittest.cc
index 53266525d8646ad61ddd29539a226085bd46e18b..a1da7c610b279e2fe4754502484104024d43f05c 100644
--- a/ash/wm/screen_dimmer_unittest.cc
+++ b/ash/wm/screen_dimmer_unittest.cc
@@ -75,13 +75,7 @@ TEST_F(ScreenDimmerTest, DimAndUndim) {
   ASSERT_EQ(nullptr, GetDimWindowLayer());
 }
 
-#if defined(OS_WIN) && !defined(USE_ASH)
-// TODO(msw): Times out on Windows. http://crbug.com/584038
-#define MAYBE_ResizeLayer DISABLED_ResizeLayer
-#else
-#define MAYBE_ResizeLayer ResizeLayer
-#endif
-TEST_F(ScreenDimmerTest, MAYBE_ResizeLayer) {
+TEST_F(ScreenDimmerTest, ResizeLayer) {
   // The dimming layer should be initially sized to cover the root window.
   dimmer_->SetDimming(true);
   ui::Layer* dimming_layer = GetDimWindowLayer();