Add compositor element id for scroll nodes in SPv2.

third_party/WebKit/Source/platform/graphics/paint/ScrollPaintPropertyNode.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 "platform/graphics/paint/ScrollPaintPropertyNode.h"
 
 #include "platform/graphics/paint/PropertyTreeState.h"
 
 namespace blink {
 
 ScrollPaintPropertyNode* ScrollPaintPropertyNode::root() {
   DEFINE_STATIC_REF(ScrollPaintPropertyNode, root,
                     (ScrollPaintPropertyNode::create(
                         nullptr, TransformPaintPropertyNode::root(), IntSize(),
                         IntSize(), false, false, 0)));
   return root;
 }
 
 String ScrollPaintPropertyNode::toString() const {
   FloatSize scrollOffset =
       m_scrollOffsetTranslation->matrix().to2DTranslation();
   std::string mainThreadScrollingReasonsAsText =
       MainThreadScrollingReason::mainThreadScrollingReasonsAsText(
           m_mainThreadScrollingReasons);
   return String::format(
       "parent=%p scrollOffsetTranslation=%s clip=%s bounds=%s "
       "userScrollableHorizontal=%s"
-      " userScrollableVertical=%s mainThreadScrollingReasons=%s",
+      " userScrollableVertical=%s mainThreadScrollingReasons=%s"
+      "compositorElementId=(%d, %d)",
       m_parent.get(), scrollOffset.toString().ascii().data(),
       m_clip.toString().ascii().data(), m_bounds.toString().ascii().data(),
       m_userScrollableHorizontal ? "yes" : "no",
       m_userScrollableVertical ? "yes" : "no",
-      mainThreadScrollingReasonsAsText.c_str());
+      mainThreadScrollingReasonsAsText.c_str(), m_compositorElementId.primaryId,
+      m_compositorElementId.secondaryId);
 }
 
 #if DCHECK_IS_ON()
 
 String ScrollPaintPropertyNode::toTreeString() const {
   return blink::PropertyTreeStatePrinter<blink::ScrollPaintPropertyNode>()
       .pathAsString(this);
 }
 
 #endif
 
 }  // namespace blink