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 932937e7973524cf552785eeac640114966954fc..5f800a020a9cfd94ded9c069f088de9766f4b58b 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) {

[chrishtr, 2015/12/01 23:17:03]

Is there a testcase for the code here?

[Ian Vollick, 2015/12/02 00:39:33]

Yes. In CompositorWorkerTest, I test three types of CompositorProxy.
 1. A proxy of a typical div (for opacity and transform).
 2. A proxy of an overflow:scrolling div (for scrollLeft and scrollTop), and
 3. A proxy of document.scrollingElement (for scrollLeft and scrollTop).

This code sets up the elementId and mutableProperties for the scrolling element
(#3 above) and the tests check that we're getting the right values. If you
search for rootScrollLayer in CompositorWorkerTest.cpp you'll see the relevant
lines.

+            if (Element* scrollingElement = m_layoutView.document().scrollingElement()) {
+                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);