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..7eaf836be2f90f2ac96e9977d2b52a1bceb5486f 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollbarTheme.cpp
+++ b/third_party/WebKit/Source/platform/scroll/ScrollbarTheme.cpp
@@ -233,6 +233,30 @@ bool ScrollbarTheme::shouldSnapBackToDragOrigin(
       scrollbar.orientation() == HorizontalScrollbar);
 }
 
+double ScrollbarTheme::overlayScrollbarFadeOutDelaySeconds() const {
+  DCHECK(usesOverlayScrollbars());
+#if !OS(MACOSX)

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

Override in ScrollbarThemeMac instead of using #if's.

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

Can't since WebThemeEngine.h is conditionally included in this file but I've
moved the themeEngine bits into ScrollbarThemeOverlay.

+  return Platform::current()
+      ->themeEngine()
+      ->getOverlayScrollbarFadeOutDelaySeconds();
+#else
+  // On Mac, fading is controlled by the painting code in ScrollAnimatorMac.
+  return 0.0;
+#endif
+}
+
+double ScrollbarTheme::overlayScrollbarFadeOutDurationSeconds() const {
+  DCHECK(usesOverlayScrollbars());
+#if !OS(MACOSX)
+  return Platform::current()
+      ->themeEngine()
+      ->getOverlayScrollbarFadeOutDurationSeconds();
+#else
+  // On Mac, fading is controlled by the painting code in ScrollAnimatorMac.
+  return 0.0;
+#endif
+}
+
 int ScrollbarTheme::thumbPosition(const ScrollbarThemeClient& scrollbar,
                                   float scrollPosition) {
   if (scrollbar.enabled()) {