Don't add subpixel accumulations for squashed layers when invalidating them.

Source/core/rendering/compositing/CompositedLayerMapping.cpp

Index: Source/core/rendering/compositing/CompositedLayerMapping.cpp
diff --git a/Source/core/rendering/compositing/CompositedLayerMapping.cpp b/Source/core/rendering/compositing/CompositedLayerMapping.cpp
index 9203eb561848719d29b7520cbed32a92cd9b371a..c2d15b716ff74d0aa319f1af1b85c0df5dc9608e 100644
--- a/Source/core/rendering/compositing/CompositedLayerMapping.cpp
+++ b/Source/core/rendering/compositing/CompositedLayerMapping.cpp
@@ -594,28 +594,27 @@ void CompositedLayerMapping::updateSquashingLayerGeometry(const LayoutPoint& off
     // The conversion between referenceLayer and the ancestor CLM is already computed as
     // offsetFromReferenceLayerToParentGraphicsLayer.
     totalSquashBounds.moveBy(offsetFromReferenceLayerToParentGraphicsLayer);
-    IntRect squashLayerBounds = enclosingIntRect(totalSquashBounds);
-    IntPoint squashLayerOrigin = squashLayerBounds.location();
-    LayoutSize squashLayerOriginInOwningLayerSpace = squashLayerOrigin - offsetFromReferenceLayerToParentGraphicsLayer;
+    const IntRect squashLayerBounds = enclosingIntRect(totalSquashBounds);
+    const IntPoint squashLayerOrigin = squashLayerBounds.location();
+    const LayoutSize squashLayerOriginInOwningLayerSpace = squashLayerOrigin - offsetFromReferenceLayerToParentGraphicsLayer;
 
     // Now that the squashing bounds are known, we can convert the RenderLayer painting offsets
     // from CLM owning layer space to the squashing layer space.
     //
     // The painting offset we want to compute for each squashed RenderLayer is essentially the position of
-    // the squashed RenderLayer described w.r.t. referenceLayer's origin. For this purpose we already cached
-    // offsetFromSquashingCLM before, which describes where the squashed RenderLayer is located w.r.t.
-    // referenceLayer. So we just need to convert that point from referenceLayer space to referenceLayer
+    // the squashed RenderLayer described w.r.t. referenceLayer's origin.
+    // So we just need to convert that point from referenceLayer space to the squashing layer's
     // space. This is simply done by subtracing squashLayerOriginInOwningLayerSpace, but then the offset
     // overall needs to be negated because that's the direction that the painting code expects the
     // offset to be.
     for (size_t i = 0; i < layers.size(); ++i) {
-        LayoutPoint offsetFromTransformedAncestorForSquashedLayer = layers[i].renderLayer->computeOffsetFromTransformedAncestor();
-        LayoutSize offsetFromSquashLayerOrigin = (offsetFromTransformedAncestorForSquashedLayer - referenceOffsetFromTransformedAncestor) - squashLayerOriginInOwningLayerSpace;
+        const LayoutPoint offsetFromTransformedAncestorForSquashedLayer = layers[i].renderLayer->computeOffsetFromTransformedAncestor();
+        const LayoutSize offsetFromSquashLayerOrigin = (offsetFromTransformedAncestorForSquashedLayer - referenceOffsetFromTransformedAncestor) - squashLayerOriginInOwningLayerSpace;
 
-        // It is ok to issue paint invalidation here, because all of the geometry needed to correctly invalidate paint is computed by this point.
         IntSize newOffsetFromRenderer = -IntSize(offsetFromSquashLayerOrigin.width().round(), offsetFromSquashLayerOrigin.height().round());
         LayoutSize subpixelAccumulation = offsetFromSquashLayerOrigin + newOffsetFromRenderer;
         if (layers[i].offsetFromRendererSet && layers[i].offsetFromRenderer != newOffsetFromRenderer) {
+            // It is ok to issue paint invalidation here, because all of the geometry needed to correctly invalidate paint is computed by this point.
             layers[i].renderLayer->renderer()->invalidatePaintIncludingNonCompositingDescendants();
 
             TRACE_LAYER_INVALIDATION(layers[i].renderLayer, InspectorLayerInvalidationTrackingEvent::SquashingLayerGeometryWasUpdated);