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

third_party/WebKit/Source/platform/testing/TestingPlatformSupport.cpp

Index: third_party/WebKit/Source/platform/testing/TestingPlatformSupport.cpp
diff --git a/third_party/WebKit/Source/platform/testing/TestingPlatformSupport.cpp b/third_party/WebKit/Source/platform/testing/TestingPlatformSupport.cpp
index e47eb909e775f34a27ecf9600517723532d14c5f..59ba94724845531dba20609b291b92d62c4ebae2 100644
--- a/third_party/WebKit/Source/platform/testing/TestingPlatformSupport.cpp
+++ b/third_party/WebKit/Source/platform/testing/TestingPlatformSupport.cpp
@@ -120,8 +120,7 @@
 TestingCompositorSupport::createScrollbarLayer(
     std::unique_ptr<WebScrollbar>,
     WebScrollbarThemePainter,
-    std::unique_ptr<WebScrollbarThemeGeometry>,
-    WebLayer* scrollLayer) {
+    std::unique_ptr<WebScrollbarThemeGeometry>) {
   return nullptr;
 }
 
@@ -129,8 +128,7 @@
 TestingCompositorSupport::createOverlayScrollbarLayer(
     std::unique_ptr<WebScrollbar>,
     WebScrollbarThemePainter,
-    std::unique_ptr<WebScrollbarThemeGeometry>,
-    WebLayer* scrollLayer) {
+    std::unique_ptr<WebScrollbarThemeGeometry>) {
   return nullptr;
 }
 
@@ -139,8 +137,7 @@
     WebScrollbar::Orientation,
     int thumbThickness,
     int trackStart,
-    bool isLeftSideVerticalScrollbar,
-    WebLayer* scrollLayer) {
+    bool isLeftSideVerticalScrollbar) {
   return nullptr;
 }