[Refactor] Moved scrollbar creation and deletion to ScrollbarManager

third_party/WebKit/Source/core/paint/PaintInvalidationCapableScrollableArea.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/paint/PaintInvalidationCapableScrollableArea.h"
 
 #include "core/frame/Settings.h"
 #include "core/frame/UseCounter.h"
 #include "core/html/HTMLFrameOwnerElement.h"
 #include "core/layout/LayoutBox.h"
@@ skipping 262 matching lines @@
                ? WebFeature::kScrollbarUseVerticalScrollbarTrack
                : WebFeature::kScrollbarUseHorizontalScrollbarTrack);
       break;
     default:
       return;
   }
 
   UseCounter::Count(GetLayoutBox()->GetDocument(), scrollbar_use_uma);
 }
 
+bool PaintInvalidationCapableScrollableArea::ShouldUseCustomScrollbars(

[skobes, 2017/06/27 18:48:15]

I think this method would make more sense on LayoutObject, with the name
HasCustomScrollbarStyle.

+    LayoutObject*& style_source) const {

[bokan, 2017/06/27 17:48:52]

This method shouldn't have an output param. The caller should call
LayoutObjectForScrollbars() if needed.

+  DCHECK(!style_source);
+  style_source = LayoutObjectForScrollbars();
+
+  return style_source && style_source->IsBox() &&
+         style_source->StyleRef().HasPseudoStyle(kPseudoIdScrollbar);
+}
+
 }  // namespace blink