Refactor the way PaintArtifactCompositor is attached and used.

third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositorTest.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/compositing/PaintArtifactCompositor.h"
 
 #include "base/test/test_simple_task_runner.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "cc/layers/layer.h"
 #include "cc/test/fake_compositor_frame_sink.h"
@@ skipping 52 matching lines @@
         : m_taskRunner(new base::TestSimpleTaskRunner)
         , m_taskRunnerHandle(m_taskRunner)
     {
     }
 
     void SetUp() override
     {
         RuntimeEnabledFeatures::setSlimmingPaintV2Enabled(true);
 
         // Delay constructing the compositor until after the feature is set.
-        m_paintArtifactCompositor = wrapUnique(new PaintArtifactCompositor);
+        m_paintArtifactCompositor = PaintArtifactCompositor::create();
         m_paintArtifactCompositor->enableExtraDataForTesting();
 
         cc::LayerTreeSettings settings = WebLayerTreeViewImplForTesting::defaultLayerTreeSettings();
         settings.single_thread_proxy_scheduler = false;
         settings.use_layer_lists = true;
         m_webLayerTreeView = wrapUnique(new WebLayerTreeViewWithCompositorFrameSink(settings));
         m_webLayerTreeView->setRootLayer(*m_paintArtifactCompositor->getWebLayer());
     }
 
     void TearDown() override
@@ skipping 527 matching lines @@
     EXPECT_TRUE(transformNodeA.local.IsIdentity());
     const cc::TransformNode& transformNodeB = *transformTree.Node(scrollNodeB.transform_id);
     EXPECT_TRUE(transformNodeB.local.IsIdentity());
 
     EXPECT_EQ(gfx::ScrollOffset(-11, -13), scrollTree.current_scroll_offset(contentLayerAt(0)->id()));
     EXPECT_EQ(gfx::ScrollOffset(-37, -41), scrollTree.current_scroll_offset(contentLayerAt(1)->id()));
 }
 
 } // namespace
 } // namespace blink