[compositor-worker] root scrolling layer is associated with document scrolling element

third_party/WebKit/Source/core/dom/CompositorProxy.cpp

Index: third_party/WebKit/Source/core/dom/CompositorProxy.cpp
diff --git a/third_party/WebKit/Source/core/dom/CompositorProxy.cpp b/third_party/WebKit/Source/core/dom/CompositorProxy.cpp
index e715638b804f420fddba14fb52c421ec4cc444a1..e0a2b215676afa2c9f745012fd47d53923af40e7 100644
--- a/third_party/WebKit/Source/core/dom/CompositorProxy.cpp
+++ b/third_party/WebKit/Source/core/dom/CompositorProxy.cpp
@@ -115,26 +115,41 @@ CompositorProxy* CompositorProxy::create(ExecutionContext* context,
     return nullptr;
   }
 
-  return new CompositorProxy(*element, attributeArray);
+  Document* document = toDocument(context);
+  Node* scrollingNode = element;
+  // The scrolling layer for the root scrolling element is attached to the
+  // document. So use document as scrolling node when creating a proxy to ensure
+  // we mutate the correct scroll layer.
+  // TODO(majidvp): Consider checking against
+  // |RootScrollerController::effectiveRootScroller| instead of
+  // |Document::scrollingElement|.
+  if (element->isSameNode(document->scrollingElement()))
+    scrollingNode = document;

[flackr, 2017/03/01 16:31:26]

It seems like the proper fix would be for cc to set the document scrolling layer
to be the body element's scrolling layer to reflect that this scrolling layer is
the scrolling element's scrolling layer. Then we wouldn't need to have a
separate id and it would match blink's concept of the scrolling element right?

I think this would mean changing the element id for the root scrolling contents
layer to be the document.scrollingElement's id in CompositedLayerMapping.cpp

+  return new CompositorProxy(*element, *scrollingNode, attributeArray);
 }
 
 CompositorProxy* CompositorProxy::create(ExecutionContext* context,
                                          uint64_t elementId,
+                                         uint64_t scrollingNodeId,
                                          uint32_t compositorMutableProperties) {
   if (context->isCompositorWorkerGlobalScope()) {
     WorkerClients* clients = toWorkerGlobalScope(context)->clients();
     DCHECK(clients);
     CompositorWorkerProxyClient* client =
         CompositorWorkerProxyClient::from(clients);
-    return new CompositorProxy(elementId, compositorMutableProperties, client);
+    return new CompositorProxy(elementId, scrollingNodeId,
+                               compositorMutableProperties, client);
   }
 
-  return new CompositorProxy(elementId, compositorMutableProperties);
+  return new CompositorProxy(elementId, scrollingNodeId,
+                             compositorMutableProperties);
 }
 
 CompositorProxy::CompositorProxy(uint64_t elementId,
+                                 uint64_t scrollingNodeId,
                                  uint32_t compositorMutableProperties)
     : m_elementId(elementId),
+      m_scrollingNodeId(scrollingNodeId),
       m_compositorMutableProperties(compositorMutableProperties),
       m_client(nullptr) {
   DCHECK(m_compositorMutableProperties);
@@ -154,16 +169,19 @@ CompositorProxy::CompositorProxy(uint64_t elementId,
 }
 
 CompositorProxy::CompositorProxy(Element& element,
+                                 Node& scrollingNode,
                                  const Vector<String>& attributeArray)
     : CompositorProxy(DOMNodeIds::idForNode(&element),
+                      DOMNodeIds::idForNode(&scrollingNode),
                       compositorMutablePropertiesFromNames(attributeArray)) {
   DCHECK(isMainThread());
 }
 
 CompositorProxy::CompositorProxy(uint64_t elementId,
+                                 uint64_t scrollingNodeId,
                                  uint32_t compositorMutableProperties,
                                  CompositorProxyClient* client)
-    : CompositorProxy(elementId, compositorMutableProperties) {
+    : CompositorProxy(elementId, scrollingNodeId, compositorMutableProperties) {
   m_client = client;
   DCHECK(m_client);
   DCHECK(isControlThread());