compositor-worker: plumb element id and mutable properties

third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp

Index: third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp b/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
index 60bd3291932ebb21ce16eeed6e41178add99419f..f496a96b7a4d77d0a9d3f80b2e4cf48e86d0ea6c 100644
--- a/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
@@ -63,6 +63,7 @@
 #include "platform/graphics/paint/PaintController.h"
 #include "platform/graphics/paint/TransformDisplayItem.h"
 #include "public/platform/Platform.h"
+#include "public/platform/WebMutableProperties.h"
 
 namespace blink {
 
@@ -391,6 +392,23 @@ void PaintLayerCompositor::updateIfNeeded()
     }
 
     if (updateType != CompositingUpdateNone) {
+        // FIXME: it should not be necessary to check that the document has no child needing a style recalc. See crbug.com/552847
+        if (RuntimeEnabledFeatures::compositorWorkerEnabled() && m_scrollLayer && !m_layoutView.document().childNeedsStyleRecalc()) {
+            Frame* mainFrame = page()->mainFrame();
+            ASSERT(mainFrame->isLocalFrame());
+            ASSERT(!m_layoutView.needsLayout());
+            if (Element* scrollingElement = m_layoutView.document().scrollingElement()) {
+                uint64_t elementId = 0;
+                uint32_t mutableProperties = WebMutablePropertyNone;
+                if (scrollingElement->hasCompositorProxy()) {
+                    elementId = DOMNodeIds::idForNode(scrollingElement);
+                    mutableProperties = WebMutablePropertyScrollLeft | WebMutablePropertyScrollTop;
+                }
+                m_scrollLayer->setElementId(elementId);
+                m_scrollLayer->setMutableProperties(mutableProperties);
+            }
+        }
+
         GraphicsLayerUpdater updater;
         updater.update(*updateRoot, layersNeedingPaintInvalidation);