Remove indirection: setup scrollbar scroll layers in the scrollbar constructor

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

Index: third_party/WebKit/Source/platform/testing/TestingPlatformSupport.h
diff --git a/third_party/WebKit/Source/platform/testing/TestingPlatformSupport.h b/third_party/WebKit/Source/platform/testing/TestingPlatformSupport.h
index 3c052d18d16f4b24a9a6f2f96e14cb77bbedf180..67bb0b82fdcd875d9215f8129be28cee1fe28357 100644
--- a/third_party/WebKit/Source/platform/testing/TestingPlatformSupport.h
+++ b/third_party/WebKit/Source/platform/testing/TestingPlatformSupport.h
@@ -76,16 +76,19 @@ class TestingCompositorSupport : public WebCompositorSupport {
   std::unique_ptr<WebScrollbarLayer> createScrollbarLayer(
       std::unique_ptr<WebScrollbar>,
       WebScrollbarThemePainter,
-      std::unique_ptr<WebScrollbarThemeGeometry>) override;
+      std::unique_ptr<WebScrollbarThemeGeometry>,
+      WebLayer* scrollLayer) override;
   std::unique_ptr<WebScrollbarLayer> createOverlayScrollbarLayer(
       std::unique_ptr<WebScrollbar>,
       WebScrollbarThemePainter,
-      std::unique_ptr<WebScrollbarThemeGeometry>) override;
+      std::unique_ptr<WebScrollbarThemeGeometry>,
+      WebLayer* scrollLayer) override;
   std::unique_ptr<WebScrollbarLayer> createSolidColorScrollbarLayer(
       WebScrollbar::Orientation,
       int thumbThickness,
       int trackStart,
-      bool isLeftSideVerticalScrollbar) override;
+      bool isLeftSideVerticalScrollbar,
+      WebLayer* scrollLayer) override;
 };
 
 // A base class to override Platform methods for testing.  You can override the