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

third_party/WebKit/Source/platform/graphics/paint/PaintArtifact.cpp

Index: third_party/WebKit/Source/platform/graphics/paint/PaintArtifact.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/paint/PaintArtifact.cpp b/third_party/WebKit/Source/platform/graphics/paint/PaintArtifact.cpp
index 920c745fe37b88d3cf555f6c12cf247802003884..d4311d6d3a2176fa0a1989755faff38fdfdaabef 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/PaintArtifact.cpp
+++ b/third_party/WebKit/Source/platform/graphics/paint/PaintArtifact.cpp
@@ -91,22 +91,28 @@ void PaintArtifact::replay(const FloatRect& bounds,
     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());
-
-    // 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);
+    replay(bounds, *graphicsContext.canvas());
   }
 }
 
+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");