Fix Compositing of Opaque Scrolling Layers and Add Tests

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 4a3d4a54238540f1a60f17931b90eb4a17fbbb44..698df571c2840948cc539a109e3bbba365b0c6c9 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
@@ -1493,11 +1493,9 @@ static bool layerNeedsCompositedScrolling(PaintLayerScrollableArea::LCDTextMode
     if (node && node->isElementNode() && (toElement(node)->compositorMutableProperties() & (CompositorMutableProperty::kScrollTop | CompositorMutableProperty::kScrollLeft)))
         return true;
 
-    // TODO(schenney) The color test alone is inadequate. When https://codereview.chromium.org/2196583002 lands
-    // we should use PaintLayer::shouldPaintBackgroundOntoForeground() because we will not still get
-    // LCD text unless the conditions there are met. It also unifies logic for scrolling compositing decisions.
     bool backgroundSupportsLCDText = RuntimeEnabledFeatures::compositeOpaqueScrollersEnabled()
-        && !layer->layoutObject()->style()->visitedDependentColor(CSSPropertyBackgroundColor).hasAlpha();
+        && layer->shouldPaintBackgroundOntoScrollingContentsLayer()
+        && layer->backgroundIsKnownToBeOpaqueInRect(toLayoutBox(layer->layoutObject())->paddingBoxRect());
     if (mode == PaintLayerScrollableArea::ConsiderLCDText
         && !layer->compositor()->preferCompositingToLCDTextEnabled()
         && !backgroundSupportsLCDText)