Add compositor element id for scroll nodes in SPv2.

third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilderTest.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/PaintPropertyTreeBuilderTest.h"
 
 #include "core/html/HTMLIFrameElement.h"
 #include "core/layout/LayoutTreeAsText.h"
 #include "core/paint/ObjectPaintProperties.h"
 #include "core/paint/PaintPropertyTreePrinter.h"
@@ skipping 3129 matching lines @@
   EXPECT_EQ(0.5f, effect->opacity());
 
   LayoutObject* target = getLayoutObjectByElementId("target");
   const auto* localBorderBoxProperties =
       target->paintProperties()->localBorderBoxProperties();
   ASSERT_TRUE(localBorderBoxProperties);
   EXPECT_EQ(LayoutPoint(66, 55), target->paintOffset());
   EXPECT_EQ(effect, localBorderBoxProperties->effect());
 }
 
+TEST_P(PaintPropertyTreeBuilderTest, ScrollNodeHasCompositorElementId) {
+  setBodyInnerHTML(
+      "<div id='target' style='overflow: auto; width: 100px; height: 100px'>"
+      "  <div style='width: 200px; height: 200px'></div>"
+      "</div>");
+
+  const ObjectPaintProperties* properties = paintPropertiesForElement("target");
+  EXPECT_TRUE(properties->scroll());
+  EXPECT_NE(CompositorElementId(), properties->scroll()->compositorElementId());
+}
+
 }  // namespace blink