Make DisplayItemClient an interface

third_party/WebKit/Source/platform/graphics/paint/ScrollDisplayItem.cpp

 // Copyright 2014 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 "config.h"
 #include "platform/graphics/paint/ScrollDisplayItem.h"
 
 #include "platform/graphics/GraphicsContext.h"
 #include "platform/transforms/AffineTransform.h"
 #include "public/platform/WebDisplayItemList.h"
 
 namespace blink {
 
 void BeginScrollDisplayItem::replay(GraphicsContext& context) const
 {
     context.save();
     context.translate(-m_currentOffset.width(), -m_currentOffset.height());
 }
 
 void BeginScrollDisplayItem::appendToWebDisplayItemList(const IntRect& visualRect, WebDisplayItemList* list) const
 {
-    WebDisplayItemList::ScrollContainerId scrollContainerId = client();
+    WebDisplayItemList::ScrollContainerId scrollContainerId = &client();
     list->appendScrollItem(visualRect, m_currentOffset, scrollContainerId);
 }
 
 #ifndef NDEBUG
 void BeginScrollDisplayItem::dumpPropertiesAsDebugString(WTF::StringBuilder& stringBuilder) const
 {
     PairedBeginDisplayItem::dumpPropertiesAsDebugString(stringBuilder);
     stringBuilder.append(WTF::String::format(", currentOffset: [%d,%d]", m_currentOffset.width(), m_currentOffset.height()));
 }
 #endif
 
 void EndScrollDisplayItem::replay(GraphicsContext& context) const
 {
     context.restore();
 }
 
 void EndScrollDisplayItem::appendToWebDisplayItemList(const IntRect& visualRect, WebDisplayItemList* list) const
 {
     list->appendEndScrollItem(visualRect);
 }
 
 } // namespace blink