[Refactor] Moved scrollbar creation and deletion to ScrollbarManager

third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp

 /*
  * Copyright (c) 2010, Google Inc. All rights reserved.
  * Copyright (C) 2008, 2011 Apple Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 378 matching lines @@
     scroll_animator->ContentAreaDidHide();
 }
 
 void ScrollableArea::FinishCurrentScrollAnimations() const {
   if (ScrollAnimatorBase* scroll_animator = ExistingScrollAnimator())
     scroll_animator->FinishCurrentScrollAnimations();
 }
 
 void ScrollableArea::DidAddScrollbar(Scrollbar& scrollbar,
                                      ScrollbarOrientation orientation) {
+  if (scrollbar.IsCustomScrollbar())
+    return;
   if (orientation == kVerticalScrollbar)
     GetScrollAnimator().DidAddVerticalScrollbar(scrollbar);
   else
     GetScrollAnimator().DidAddHorizontalScrollbar(scrollbar);
 
   // <rdar://problem/9797253> AppKit resets the scrollbar's style when you
   // attach a scrollbar
   SetScrollbarOverlayColorTheme(GetScrollbarOverlayColorTheme());
 }
 
 void ScrollableArea::WillRemoveScrollbar(Scrollbar& scrollbar,
                                          ScrollbarOrientation orientation) {
+  if (scrollbar.IsCustomScrollbar())
+    return;
   if (ScrollAnimatorBase* scroll_animator = ExistingScrollAnimator()) {
     if (orientation == kVerticalScrollbar)
       scroll_animator->WillRemoveVerticalScrollbar(scrollbar);
     else
       scroll_animator->WillRemoveHorizontalScrollbar(scrollbar);
   }
 }
 
 void ScrollableArea::ContentsResized() {
   if (ScrollAnimatorBase* scroll_animator = ExistingScrollAnimator())
@@ skipping 269 matching lines @@
                                          offset.y() - ScrollOrigin().Y());
   SetScrollOffset(new_offset, kCompositorScroll);
 }
 
 DEFINE_TRACE(ScrollableArea) {
   visitor->Trace(scroll_animator_);
   visitor->Trace(programmatic_scroll_animator_);
 }
 
 }  // namespace blink