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 aa46e43940742b229900fa201650938a29b61626..4d51ad8492608c19051a85577b3b301929fe85e4 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 +392,20 @@ 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()) {

[chrishtr, 2015/11/24 16:22:50]

What is actually happening? Let's squash this bug now.

[Ian Vollick, 2015/11/25 18:28:45]

This is an old, unrelated video bug
(https://code.google.com/p/chromium/issues/detail?id=372245).
LayoutTextTrackContainerElement changes style information during layout. The
consequence is that when we ask for the scrollingElement after layout, it
sometimes complains in debug mode due to an assertion about dirty style. IIUC,
fixing this properly involves getting a w3c spec change made related to video
height/width.

I've changed my approach in the latest patch set. Rather than putting the
workaround in shipping code here, I've exposed the compositor worker feature via
InternalSettings so that I can disable it only for the two video layout tests
that invoke this style-update-during-layout behavior, tests that are closely
related to the linked bug.

+            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;
+                }
+                m_scrollLayer->setElementId(elementId);
+                m_scrollLayer->setMutableProperties(mutableProperties);
+            }
+        }
+
         GraphicsLayerUpdater updater;
         updater.update(*updateRoot, layersNeedingPaintInvalidation);