Implement overlay scrollbar fade out for non-composited scrollers.

third_party/WebKit/Source/platform/scroll/ScrollbarTheme.cpp

Index: third_party/WebKit/Source/platform/scroll/ScrollbarTheme.cpp
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollbarTheme.cpp b/third_party/WebKit/Source/platform/scroll/ScrollbarTheme.cpp
index 9d36150257e4681000f95dbb1da3bee179bc2e3d..6579fe491766dc6ef2c702aedbb0000f56081906 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollbarTheme.cpp
+++ b/third_party/WebKit/Source/platform/scroll/ScrollbarTheme.cpp
@@ -233,6 +233,16 @@ bool ScrollbarTheme::shouldSnapBackToDragOrigin(
       scrollbar.orientation() == HorizontalScrollbar);
 }
 
+double ScrollbarTheme::overlayScrollbarFadeOutDelaySeconds() const {
+  // On Mac, fading is controlled by the painting code in ScrollAnimatorMac.
+  return 0.0;
+}
+
+double ScrollbarTheme::overlayScrollbarFadeOutDurationSeconds() const {
+  // On Mac, fading is controlled by the painting code in ScrollAnimatorMac.
+  return 0.0;
+}
+
 int ScrollbarTheme::thumbPosition(const ScrollbarThemeClient& scrollbar,
                                   float scrollPosition) {
   if (scrollbar.enabled()) {