[Refactor] Moved scrollbar creation and deletion to ScrollbarManager

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

 // Copyright 2016 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/ScrollbarManager.h"
 
+#include "core/frame/LocalFrame.h"
+#include "core/frame/LocalFrameView.h"
+#include "core/layout/LayoutBox.h"
+#include "core/layout/LayoutObject.h"
+#include "core/layout/LayoutScrollbar.h"
+#include "core/layout/LayoutTheme.h"
+#include "core/page/ChromeClient.h"
+#include "core/page/Page.h"
+#include "core/paint/PaintLayerScrollableArea.h"
+
 namespace blink {
 
 ScrollbarManager::ScrollbarManager(ScrollableArea& scrollable_area)
     : scrollable_area_(&scrollable_area),
       h_bar_is_attached_(0),
       v_bar_is_attached_(0) {}
 
 DEFINE_TRACE(ScrollbarManager) {
   visitor->Trace(scrollable_area_);
   visitor->Trace(h_bar_);
   visitor->Trace(v_bar_);
 }
 
 void ScrollbarManager::Dispose() {
   h_bar_is_attached_ = v_bar_is_attached_ = 0;
   DestroyScrollbar(kHorizontalScrollbar);
   DestroyScrollbar(kVerticalScrollbar);
 }
 
+Scrollbar* ScrollbarManager::CreateScrollbar(ScrollbarOrientation orientation) {

[szager1, 2017/06/27 20:42:13]

All of this logic could be moved into PLSA and FrameView, to allow moving
ScrollbarManager into platform.

+  DCHECK(scrollable_area_->GetLayoutBox());
+  DCHECK(orientation == kHorizontalScrollbar ? !h_bar_is_attached_
+                                             : !v_bar_is_attached_);
+  LayoutObject* actual_layout_object = nullptr;

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

layout_object_for_style

+
+  Scrollbar* scrollbar = nullptr;
+  if (scrollable_area_->ShouldUseCustomScrollbars(actual_layout_object)) {
+    scrollbar = LayoutScrollbar::CreateCustomScrollbar(
+        scrollable_area_.Get(), orientation,
+        ToElement(actual_layout_object->GetNode()));

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

Add a DCHECK that if we're using custom scrollbars, the layout object isn't a
LayoutView.

+  } else {
+    ScrollbarControlSize scrollbar_size = kRegularScrollbar;
+
+    if (actual_layout_object &&
+        actual_layout_object->StyleRef().HasAppearance() &&
+        scrollable_area_->IsPaintLayerScrollableArea()) {
+      scrollbar_size = LayoutTheme::GetTheme().ScrollbarControlSizeForPart(
+          actual_layout_object->StyleRef().Appearance());
+    }
+
+    scrollbar =
+        Scrollbar::Create(scrollable_area_.Get(), orientation, scrollbar_size,
+                          &scrollable_area_->GetLayoutBox()
+                               ->GetFrame()
+                               ->GetPage()
+                               ->GetChromeClient());
+  }
+
+  scrollable_area_->GetLayoutBox()->GetDocument().View()->AddScrollbar(
+      scrollbar);
+
+  return scrollbar;
+}
+
+void ScrollbarManager::DestroyScrollbar(ScrollbarOrientation orientation) {
+  Member<Scrollbar>& scrollbar =
+      orientation == kHorizontalScrollbar ? h_bar_ : v_bar_;
+  DCHECK(orientation == kHorizontalScrollbar ? !h_bar_is_attached_
+                                             : !v_bar_is_attached_);
+  if (!scrollbar)
+    return;
+
+  scrollable_area_->WillRemoveScrollbar(*scrollbar, orientation);

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

This used to only be called only for non-custom scrollbars but I think it should
be fine to call for custom too (and better to do that). Could you please just
confirm that this doesn't blow up in an obvious way for custom scrollbars?

+
+  scrollable_area_->GetLayoutBox()->GetDocument().View()->RemoveScrollbar(
+      scrollbar);
+
+  scrollbar->DisconnectFromScrollableArea();
+  scrollbar = nullptr;
+}
+
 }  // namespace blink