Implement overlay scrollbar fade out for non-composited scrollers.

ui/native_theme/native_theme_aura.cc

Index: ui/native_theme/native_theme_aura.cc
diff --git a/ui/native_theme/native_theme_aura.cc b/ui/native_theme/native_theme_aura.cc
index dc7166e6c491181340db32218f2f768dc48c7bab..6fa6f6c86569a1a8f01ced5a92034c5b7822c305 100644
--- a/ui/native_theme/native_theme_aura.cc
+++ b/ui/native_theme/native_theme_aura.cc
@@ -197,6 +197,9 @@ void NativeThemeAura::PaintScrollbarThumb(
   SkAlpha thumb_alpha = ThumbAlphaForState(state);
 
   if (IsOverlayScrollbarEnabled()) {
+    if (state == kDisabled)

[skobes, 2016/11/02 21:02:43]

This seems redundant with an identical check at the top of the function.

[bokan, 2016/11/02 22:41:57]

Doh! Missed that :)

+      return;
+
     thumb_color = kOverlayScrollbarThumbColor[theme];
 
     // In overlay mode, draw a stroke (border).