Fold compositing display items into contained drawings if the drawing is a singleton.

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

Index: third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp b/third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp
index 3ab41c686c1216055d6ea59218eb117d4a4a73ee..29eb7671182720f86a2ffa23103fab8d2fdf281a 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp
+++ b/third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp
@@ -155,6 +155,13 @@ void PaintController::removeLastDisplayItem()
         m_newPaintChunks.decrementDisplayItemIndex();
 }
 
+const DisplayItem* PaintController::lastDisplayItem(unsigned offset)
+{
+    if (offset < m_newDisplayItemList.size())
+        return &m_newDisplayItemList[m_newDisplayItemList.size() - offset - 1];
+    return nullptr;
+}
+
 void PaintController::processNewItem(DisplayItem& displayItem)
 {
     DCHECK(!m_constructionDisabled);