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 6d1bf5e6804f771ffa97a4784cc174588667985c..b3bb5511694b3d2035c40d8b161464fde62481ca 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/WebCompositorMutableProperties.h"
 
 namespace blink {
 
@@ -391,6 +392,19 @@ void PaintLayerCompositor::updateIfNeeded()
     }
 
     if (updateType != CompositingUpdateNone) {
+        if (RuntimeEnabledFeatures::compositorWorkerEnabled() && m_scrollLayer) {
+            if (Element* scrollingElement = m_layoutView.document().scrollingElement()) {

[esprehn, 2015/12/02 03:28:49]

why do we need special treatment for the document level scrolling element?
shouldn't this be generic to all scrolling elements?

[Ian Vollick, 2015/12/03 17:54:43]

Once we have skobes' root layer scrolling, this should be unnecessary. As it
stands, overflow scrolling and frame scrolling are treated differently today.

+                uint64_t elementId = 0;
+                uint32_t mutableProperties = WebCompositorMutablePropertyNone;
+                if (scrollingElement->hasCompositorProxy()) {
+                    elementId = DOMNodeIds::idForNode(scrollingElement);
+                    mutableProperties = (WebCompositorMutablePropertyScrollLeft | WebCompositorMutablePropertyScrollTop) & scrollingElement->compositorMutableProperties();
+                }
+                m_scrollLayer->setElementId(elementId);
+                m_scrollLayer->setCompositorMutableProperties(mutableProperties);
+            }
+        }
+
         GraphicsLayerUpdater updater;
         updater.update(*updateRoot, layersNeedingPaintInvalidation);