Use element id's for animations

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 58a1ff7a906827e2aca5ae432dd0daef1d512b24..1de7c1baa5244e1248234ec3998bc257c2816b50 100644
--- a/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
@@ -405,13 +405,9 @@ void PaintLayerCompositor::updateIfNeeded()
     if (updateType != CompositingUpdateNone) {
         if (RuntimeEnabledFeatures::compositorWorkerEnabled() && m_scrollLayer) {
             if (Element* scrollingElement = m_layoutView.document().scrollingElement()) {
-                uint64_t elementId = 0;
                 uint32_t mutableProperties = CompositorMutableProperty::kNone;
-                if (scrollingElement->hasCompositorProxy()) {
-                    elementId = DOMNodeIds::idForNode(scrollingElement);
+                if (scrollingElement->hasCompositorProxy())
                     mutableProperties = (CompositorMutableProperty::kScrollLeft | CompositorMutableProperty::kScrollTop) & scrollingElement->compositorMutableProperties();
-                }
-                m_scrollLayer->setElementId(elementId);
                 m_scrollLayer->setCompositorMutableProperties(mutableProperties);
             }
         }
@@ -1053,6 +1049,8 @@ void PaintLayerCompositor::ensureRootLayer()
         if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())
             scrollingCoordinator->setLayerIsContainerForFixedPositionLayers(m_scrollLayer.get(), true);
 
+        m_scrollLayer->setElementId(CompositorElementId(DOMNodeIds::idForNode(&m_layoutView.document()) | kScrollSubElement));

[Ian Vollick, 2016/06/01 18:08:26]

NB: here as well.

+
         // Hook them up
         m_overflowControlsHostLayer->addChild(m_containerLayer.get());
         m_containerLayer->addChild(m_scrollLayer.get());