Implement overlay scrollbar fade out for non-composited scrollers.

content/child/webthemeengine_impl_android.cc

Index: content/child/webthemeengine_impl_android.cc
diff --git a/content/child/webthemeengine_impl_android.cc b/content/child/webthemeengine_impl_android.cc
index 7db2ef4317423a779c9b28dac2cc5406c0bedc1b..3dc2f92fe063e5b0ff31f5eced3cf32f30c1d9c3 100644
--- a/content/child/webthemeengine_impl_android.cc
+++ b/content/child/webthemeengine_impl_android.cc
@@ -173,6 +173,10 @@ blink::WebSize WebThemeEngineImpl::getSize(WebThemeEngine::Part part) {
 }
 
 void WebThemeEngineImpl::getOverlayScrollbarStyle(ScrollbarStyle* style) {
+  // TODO(bokan): Android scrollbars on non-composited scrollers don't
+  // currently fade out so the fadeOutDuration and Delay  Now that this has
+  // been added into Blink for other platforms we should plumb that through for
+  // Android as well.
   if (getMajorVersion() >= kVersionLollipop) {
     style->thumbThickness = 4;
     style->scrollbarMargin = 0;