Slimming Paint phase 2 compositing algorithm plumbing & skeleton display list API.

Source/platform/graphics/ContentLayerDelegate.cpp

Index: Source/platform/graphics/ContentLayerDelegate.cpp
diff --git a/Source/platform/graphics/ContentLayerDelegate.cpp b/Source/platform/graphics/ContentLayerDelegate.cpp
index 657ecb92854104a0c810de448a4d56e21085ef67..ee11c43bd5876140c25da2fa7a60e237d23ec6eb 100644
--- a/Source/platform/graphics/ContentLayerDelegate.cpp
+++ b/Source/platform/graphics/ContentLayerDelegate.cpp
@@ -33,6 +33,7 @@
 #include "platform/geometry/IntRect.h"
 #include "platform/graphics/GraphicsContext.h"
 #include "platform/graphics/paint/DisplayItemList.h"
+#include "platform/graphics/paint/DisplayList.h"
 #include "platform/transforms/AffineTransform.h"
 #include "platform/transforms/TransformationMatrix.h"
 #include "public/platform/WebDisplayItemList.h"
@@ -90,6 +91,16 @@ void ContentLayerDelegate::paintContents(
 
     ASSERT(RuntimeEnabledFeatures::slimmingPaintEnabled());
 
+    if (RuntimeEnabledFeatures::slimmingPaintCompositorLayerizationEnabled()) {
+        // Scrollbars for the root frame stil paint in the old way, and don't have a displayList().
+        if (m_painter->displayList()) {
+            for (unsigned i = 0; i < m_painter->displayList()->size(); i++) {
+                m_painter->displayList()->displayItemInternal(i).appendToWebDisplayItemList(webDisplayItemList);
+            }
+            return;
+        }
+    }
+
     DisplayItemList* displayItemList = m_painter->displayItemList();
     ASSERT(displayItemList);
     displayItemList->setDisplayItemConstructionIsDisabled(
@@ -116,4 +127,14 @@ size_t ContentLayerDelegate::approximateUnsharedMemoryUsage() const
     return m_painter->displayItemList()->approximateUnsharedMemoryUsage();
 }
 
+const WebDisplayList* ContentLayerDelegate::displayList() const
+{
+    return m_painter->displayList();
+}
+
+const WebDisplayItemTransformTree* ContentLayerDelegate::transformTree() const
+{
+    return 0;
+}
+
 } // namespace blink