Feed ScrollableArea::showOverlayScrollbars into ScrollbarAnimationController.

third_party/WebKit/public/platform/WebLayer.h

Index: third_party/WebKit/public/platform/WebLayer.h
diff --git a/third_party/WebKit/public/platform/WebLayer.h b/third_party/WebKit/public/platform/WebLayer.h
index 806e2bf26d360a88a96a3ef040574f41125a45b5..848fe1ab64fe53c2197dc54f3b9890f814b57a11 100644
--- a/third_party/WebKit/public/platform/WebLayer.h
+++ b/third_party/WebKit/public/platform/WebLayer.h
@@ -222,6 +222,9 @@ class WebLayer {
   virtual uint32_t compositorMutableProperties() const = 0;
 
   virtual void setHasWillChangeTransformHint(bool) = 0;
+
+  // Called on the scroll layer to trigger showing the overlay scrollbars.
+  virtual void showScrollbars() = 0;
 };
 
 }  // namespace blink