Introduce RenderingTest::getLayoutObjectByElementId().

third_party/WebKit/Source/core/layout/LayoutObjectTest.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/layout/LayoutObject.h"
 
 #include "core/layout/LayoutTestHelper.h"
 #include "core/layout/LayoutView.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ skipping 95 matching lines @@
     EXPECT_EQ(layoutObject->containingBlock(), bodyLayoutObject);
 }
 
 TEST_F(LayoutObjectTest, MapToVisibleRectInContainerSpace)
 {
     setBodyInnerHTML(
         "<div id='container' style='overflow: scroll; will-change: transform; width: 50px; height: 50px'>"
         "  <span><img style='width: 20px; height: 100px'></span>"
         "  text text text text text text text"
         "</div>");
-    LayoutBlock* container = toLayoutBlock(document().getElementById("container")->layoutObject());
+    LayoutBlock* container = toLayoutBlock(getLayoutObjectByElementId("container"));
     LayoutText* text = toLayoutText(container->lastChild());
 
     container->setScrollTop(LayoutUnit(50));
     LayoutRect rect(0, 60, 20, 20);
     text->mapToVisibleRectInAncestorSpace(container, rect, nullptr);
     EXPECT_TRUE(rect == LayoutRect(0, 10, 20, 20));
 }
 
 } // namespace blink