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

Source/core/frame/FrameView.cpp

Index: Source/core/frame/FrameView.cpp
diff --git a/Source/core/frame/FrameView.cpp b/Source/core/frame/FrameView.cpp
index 502b7651f7e56a73e9f769bb0d15f57d2c667cfd..1d47f0a08048c2108107b766005b72df1e4b6cc1 100644
--- a/Source/core/frame/FrameView.cpp
+++ b/Source/core/frame/FrameView.cpp
@@ -29,6 +29,7 @@
 
 #include "core/HTMLNames.h"
 #include "core/MediaTypeNames.h"
+#include "core/compositing/DisplayListCompositingBuilder.h"
 #include "core/css/FontFaceSet.h"
 #include "core/css/resolver/StyleResolver.h"
 #include "core/dom/AXObjectCache.h"
@@ -2458,9 +2459,16 @@ void FrameView::updateLifecycleToCompositingCleanPlusScrolling()
 {
     frame().localFrameRoot()->view()->updateStyleAndLayoutIfNeededRecursive();
     LayoutView* view = layoutView();
-    if (view)
+    if (view) {
+        // If SlimmingPaintCompositorLayerizationEnabled is on, we still need this to set up the root layer(s).
         view->compositor()->updateIfNeededRecursive();
-    scrollContentsIfNeededRecursive();
+
+        if (RuntimeEnabledFeatures::slimmingPaintCompositorLayerizationEnabled()) {
+            invalidateTreeIfNeededRecursive();
+            paintAndComposite();
+        }
+        scrollContentsIfNeededRecursive();
+    }
 
     ASSERT(lifecycle().state() >= DocumentLifecycle::CompositingClean);
 }
@@ -2478,16 +2486,45 @@ void FrameView::updateAllLifecyclePhasesInternal()
     LayoutView* view = layoutView();
     if (view) {
         TRACE_EVENT1("devtools.timeline", "UpdateLayerTree", "data", InspectorUpdateLayerTreeEvent::data(m_frame.get()));
-
+        // If SlimmingPaintCompositorLayerizationEnabled is on, we still need this to set up the root layer(s).
         view->compositor()->updateIfNeededRecursive();
+
+        if (RuntimeEnabledFeatures::slimmingPaintCompositorLayerizationEnabled()) {
+            invalidateTreeIfNeededRecursive();
+            paintAndComposite();
+        }
         scrollContentsIfNeededRecursive();
-        invalidateTreeIfNeededRecursive();
         updatePostLifecycleData();
 
         ASSERT(!view->hasPendingSelection());
     }
 
-    ASSERT(lifecycle().state() == DocumentLifecycle::PaintInvalidationClean);
+    ASSERT(lifecycle().state() == DocumentLifecycle::PaintInvalidationClean
+        || (RuntimeEnabledFeatures::slimmingPaintCompositorLayerizationEnabled() && lifecycle().state() == DocumentLifecycle::CompositingClean));
+}
+
+void FrameView::paintAndComposite()
+{
+    ASSERT(frame() == page()->mainFrame() || (!frame().tree().parent()->isLocalFrame()));
+    LayoutView* view = layoutView();
+    ASSERT(view);
+    GraphicsLayer* rootGraphicsLayer = view->layer()->graphicsLayerBacking();
+    // Detached frames can have no root graphics layer.
+    if (!rootGraphicsLayer)
+        return;
+
+    GraphicsContext context(rootGraphicsLayer->displayItemList());
+    rootGraphicsLayer->paint(context);
+
+    DisplayListDiff displayListDiff;
+    rootGraphicsLayer->displayItemList()->commitNewDisplayItems(&displayListDiff);
+
+    lifecycle().advanceTo(DocumentLifecycle::InCompositingUpdate);
+
+    DisplayListCompositingBuilder compositingBuilder(*rootGraphicsLayer->displayItemList(), displayListDiff, *rootGraphicsLayer);
+    compositingBuilder.build();
+
+    lifecycle().advanceTo(DocumentLifecycle::CompositingClean);
 }
 
 void FrameView::updatePostLifecycleData()