Allow certain SP recorder classes to defer their "begin" operation.

Source/core/paint/LayerClipRecorder.cpp

Index: Source/core/paint/LayerClipRecorder.cpp
diff --git a/Source/core/paint/LayerClipRecorder.cpp b/Source/core/paint/LayerClipRecorder.cpp
index 8ed407eb3a00945912f0a74413a992922bf1cfe9..2fe66afd52c41522aff98a69737c938302f9541b 100644
--- a/Source/core/paint/LayerClipRecorder.cpp
+++ b/Source/core/paint/LayerClipRecorder.cpp
@@ -17,24 +17,19 @@
 
 namespace blink {
 
-LayerClipRecorder::LayerClipRecorder(GraphicsContext& graphicsContext, const LayoutBoxModelObject& layoutObject, DisplayItem::Type clipType, const ClipRect& clipRect,
-    const DeprecatedPaintLayerPaintingInfo* localPaintingInfo, const LayoutPoint& fragmentOffset, PaintLayerFlags paintFlags, BorderRadiusClippingRule rule)
+LayerClipRecorder::LayerClipRecorder(GraphicsContext& graphicsContext, DisplayItem::Type clipType)
     : m_graphicsContext(graphicsContext)
-    , m_layoutObject(layoutObject)
+    , m_layoutObject(nullptr)
     , m_clipType(clipType)
+    , m_engaged(false)
 {
-    IntRect snappedClipRect = pixelSnappedIntRect(clipRect.rect());
-    OwnPtr<ClipDisplayItem> clipDisplayItem = ClipDisplayItem::create(layoutObject, clipType, snappedClipRect);
-    if (localPaintingInfo && clipRect.hasRadius())
-        collectRoundedRectClips(*layoutObject.layer(), *localPaintingInfo, graphicsContext, fragmentOffset, paintFlags, rule, clipDisplayItem->roundedRectClips());
-    if (!RuntimeEnabledFeatures::slimmingPaintEnabled()) {
-        clipDisplayItem->replay(graphicsContext);
-    } else {
-        ASSERT(m_graphicsContext.displayItemList());
-        if (m_graphicsContext.displayItemList()->displayItemConstructionIsDisabled())
-            return;
-        m_graphicsContext.displayItemList()->add(clipDisplayItem.release());
-    }
+}
+
+LayerClipRecorder::LayerClipRecorder(GraphicsContext& graphicsContext, const LayoutBoxModelObject& layoutObject, DisplayItem::Type clipType, const ClipRect& clipRect,
+    const DeprecatedPaintLayerPaintingInfo* localPaintingInfo, const LayoutPoint& fragmentOffset, PaintLayerFlags paintFlags, BorderRadiusClippingRule rule)
+    : LayerClipRecorder(graphicsContext, clipType)
+{
+    begin(layoutObject, clipRect, localPaintingInfo, fragmentOffset, paintFlags, rule);
 }
 
 static bool inContainingBlockChain(DeprecatedPaintLayer* startLayer, DeprecatedPaintLayer* endLayer)
@@ -78,16 +73,39 @@ void LayerClipRecorder::collectRoundedRectClips(DeprecatedPaintLayer& paintLayer
 
 LayerClipRecorder::~LayerClipRecorder()
 {
+    if (!m_engaged)
+        return;
+
     if (RuntimeEnabledFeatures::slimmingPaintEnabled()) {
         ASSERT(m_graphicsContext.displayItemList());
         if (m_graphicsContext.displayItemList()->displayItemConstructionIsDisabled())
             return;
         DisplayItem::Type endType = DisplayItem::clipTypeToEndClipType(m_clipType);
-        OwnPtr<EndClipDisplayItem> endClip = EndClipDisplayItem::create(m_layoutObject, endType);
+        OwnPtr<EndClipDisplayItem> endClip = EndClipDisplayItem::create(*m_layoutObject, endType);
         m_graphicsContext.displayItemList()->add(endClip.release());
     } else {
         m_graphicsContext.restore();
     }
 }
 
+void LayerClipRecorder::begin(const LayoutBoxModelObject& layoutObject, const ClipRect& clipRect, const DeprecatedPaintLayerPaintingInfo* localPaintingInfo, const LayoutPoint& fragmentOffset, PaintLayerFlags paintFlags, BorderRadiusClippingRule rule)
+{
+    ASSERT(!m_engaged);
+    m_engaged = true;
+    m_layoutObject = &layoutObject;
+
+    IntRect snappedClipRect = pixelSnappedIntRect(clipRect.rect());
+    OwnPtr<ClipDisplayItem> clipDisplayItem = ClipDisplayItem::create(*m_layoutObject, m_clipType, snappedClipRect);
+    if (localPaintingInfo && clipRect.hasRadius())
+        collectRoundedRectClips(*m_layoutObject->layer(), *localPaintingInfo, m_graphicsContext, fragmentOffset, paintFlags, rule, clipDisplayItem->roundedRectClips());
+    if (!RuntimeEnabledFeatures::slimmingPaintEnabled()) {
+        clipDisplayItem->replay(m_graphicsContext);
+    } else {
+        ASSERT(m_graphicsContext.displayItemList());
+        if (m_graphicsContext.displayItemList()->displayItemConstructionIsDisabled())
+            return;
+        m_graphicsContext.displayItemList()->add(clipDisplayItem.release());
+    }
+}
+
 } // namespace blink