Add optional debugging output of what paint chunks go into what layers.

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 76 matching lines @@
     return *m_webLayerTreeView->layerTreeHost()
                 ->GetLayerTree()
                 ->property_trees();
   }
 
   const cc::TransformNode& transformNode(const cc::Layer* layer) {
     return *propertyTrees().transform_tree.Node(layer->transform_tree_index());
   }
 
   void update(const PaintArtifact& artifact) {
-    m_paintArtifactCompositor->update(artifact, nullptr);
+    m_paintArtifactCompositor->update(artifact, nullptr, false);
     m_webLayerTreeView->layerTreeHost()->LayoutAndUpdateLayers();
   }
 
   cc::Layer* rootLayer() { return m_paintArtifactCompositor->rootLayer(); }
 
   size_t contentLayerCount() {
     return m_paintArtifactCompositor->getExtraDataForTesting()
         ->contentLayers.size();
   }
 
@@ skipping 607 matching lines @@
             scrollTree.current_scroll_offset(contentLayerAt(1)->id()));
 
   EXPECT_TRUE(scrollNodeA.main_thread_scrolling_reasons &
               MainThreadScrollingReason::kHasBackgroundAttachmentFixedObjects);
   EXPECT_FALSE(scrollNodeB.main_thread_scrolling_reasons &
                MainThreadScrollingReason::kHasBackgroundAttachmentFixedObjects);
 }
 
 }  // namespace
 }  // namespace blink