Revert of Remove indirection: setup scrollbar scroll layers in the scrollbar constructor

third_party/WebKit/Source/core/frame/VisualViewport.h

Index: third_party/WebKit/Source/core/frame/VisualViewport.h
diff --git a/third_party/WebKit/Source/core/frame/VisualViewport.h b/third_party/WebKit/Source/core/frame/VisualViewport.h
index fc6ee3067e9cc4a61599a6f7a16e7f40060c84d3..3a0afe6b26eced4f7b1da621d1a31ecda20cb535 100644
--- a/third_party/WebKit/Source/core/frame/VisualViewport.h
+++ b/third_party/WebKit/Source/core/frame/VisualViewport.h
@@ -44,6 +44,7 @@
 
 namespace blink {
 class WebScrollbarLayer;
+class WebLayer;
 }
 
 namespace blink {
@@ -118,6 +119,8 @@
   // around the point specified by anchor in window coordinates. Returns false
   // if page scale factor is left unchanged.
   bool magnifyScaleAroundAnchor(float magnifyDelta, const FloatPoint& anchor);
+
+  void setScrollLayerOnScrollbars(WebLayer*) const;
 
   // The portion of the unzoomed frame visible in the visual viewport,
   // in partial CSS pixels. Relative to the main frame.