Draw recorded content directly into the containing PaintCanvas, when possible.

third_party/WebKit/Source/platform/graphics/paint/PaintArtifact.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 "platform/graphics/paint/PaintArtifact.h"
 
 #include "cc/paint/display_item_list.h"
 #include "platform/geometry/IntRect.h"
 #include "platform/graphics/GraphicsLayer.h"
 #include "platform/graphics/compositing/PaintChunksToCcLayer.h"
@@ skipping 73 matching lines @@
          m_paintChunks.capacity() * sizeof(m_paintChunks[0]);
 }
 
 void PaintArtifact::replay(const FloatRect& bounds,
                            GraphicsContext& graphicsContext) const {
   TRACE_EVENT0("blink,benchmark", "PaintArtifact::replay");
   if (!RuntimeEnabledFeatures::slimmingPaintV2Enabled()) {
     for (const DisplayItem& displayItem : m_displayItemList)
       displayItem.replay(graphicsContext);
   } else {
-    std::unique_ptr<GeometryMapper> geometryMapper = GeometryMapper::create();
-    Vector<const PaintChunk*> pointerPaintChunks;
-    pointerPaintChunks.reserveInitialCapacity(paintChunks().size());
+    replay(bounds, *graphicsContext.canvas());
+  }
+}
 
-    // TODO(chrishtr): it's sad to have to copy this vector just to turn
-    // references into pointers.
-    for (const auto& chunk : paintChunks())
-      pointerPaintChunks.push_back(&chunk);
-    scoped_refptr<cc::DisplayItemList> displayItemList =
-        PaintChunksToCcLayer::convert(
-            pointerPaintChunks, PropertyTreeState::root(), gfx::Vector2dF(),
-            getDisplayItemList(), *geometryMapper);
-    graphicsContext.canvas()->drawDisplayItemList(displayItemList);
-  }
+void PaintArtifact::replay(const FloatRect& bounds, PaintCanvas& canvas) const {
+  TRACE_EVENT0("blink,benchmark", "PaintArtifact::replay");
+  DCHECK(RuntimeEnabledFeatures::slimmingPaintV2Enabled());
+  std::unique_ptr<GeometryMapper> geometryMapper = GeometryMapper::create();

[wkorman, 2017/04/01 00:32:40]

Separate from this change but commenting while reading -- why do we disallow
stack allocation of GeometryMapper which seems like it would be beneficial for
cases like this?

I think (conv w/ Vlad a while back) that at least parts of cc were moving away
from Create methods like we have currently for GeometryMapper where ctor is
simple like this and takes no params. Can discuss further in person sometime.

[chrishtr, 2017/04/01 04:05:25]

A good question. I don't think there is a good reason.

+  Vector<const PaintChunk*> pointerPaintChunks;
+  pointerPaintChunks.reserveInitialCapacity(paintChunks().size());
+
+  // TODO(chrishtr): it's sad to have to copy this vector just to turn
+  // references into pointers.
+  for (const auto& chunk : paintChunks())
+    pointerPaintChunks.push_back(&chunk);
+  scoped_refptr<cc::DisplayItemList> displayItemList =
+      PaintChunksToCcLayer::convert(pointerPaintChunks,
+                                    PropertyTreeState::root(), gfx::Vector2dF(),
+                                    getDisplayItemList(), *geometryMapper);
+  canvas.drawDisplayItemList(displayItemList);
 }
 
 DISABLE_CFI_PERF
 void PaintArtifact::appendToWebDisplayItemList(WebDisplayItemList* list) const {
   TRACE_EVENT0("blink,benchmark", "PaintArtifact::appendToWebDisplayItemList");
   size_t visualRectIndex = 0;
   for (const DisplayItem& displayItem : m_displayItemList) {
     displayItem.appendToWebDisplayItemList(
         m_displayItemList.visualRect(visualRectIndex), list);
     visualRectIndex++;
   }
   list->setIsSuitableForGpuRasterization(isSuitableForGpuRasterization());
 }
 
 }  // namespace blink