compositor-worker: plumb element id and mutable properties

third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp

Index: third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
index 29ab883ec348664c08b3a50d519bcd217cdea14f..12973f21307941c0d0f9db9ea99c55999efa9366 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
@@ -75,6 +75,7 @@
 #include "platform/scroll/ScrollAnimatorBase.h"
 #include "platform/scroll/ScrollbarTheme.h"
 #include "public/platform/Platform.h"
+#include "public/platform/WebCompositorMutableProperties.h"
 
 namespace blink {
 
@@ -1381,11 +1382,17 @@ bool PaintLayerScrollableArea::usesCompositedScrolling() const
 
 static bool layerNeedsCompositedScrolling(PaintLayerScrollableArea::LCDTextMode mode, const PaintLayer* layer)
 {
+    if (!layer->scrollsOverflow())
+        return false;
+
+    Node* node = layer->enclosingElement();

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

heh, enclosingElement needs to be renamed enclosingNode I guess? this code looks
busted since you assign to a Node*, then check isElementNode

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

Sounds good. Here's a cleanup cl for that:
https://codereview.chromium.org/1495053002

[Ian Vollick, 2015/12/03 22:33:02]

enclosingNode been landed and I've rebased this change. It looks less silly :)

+    if (node && node->isElementNode() && (toElement(node)->compositorMutableProperties() & (WebCompositorMutablePropertyScrollTop | WebCompositorMutablePropertyScrollLeft)))
+        return true;
+
     if (mode == PaintLayerScrollableArea::ConsiderLCDText && !layer->compositor()->preferCompositingToLCDTextEnabled())
         return false;
 
-    return layer->scrollsOverflow()
-        && !layer->hasDescendantWithClipPath()
+    return !layer->hasDescendantWithClipPath()
         && !layer->hasAncestorWithClipPath()
         && !layer->layoutObject()->style()->hasBorderRadius();
 }