Let synchronized painting generate correct paint invalidation rects

third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp

Index: third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp b/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp
index aefc55559d2a83e8151df2f99fb89ecae2d5727c..bb046b04f4fafd3a2ee0c8c7006b841543b28278 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp
@@ -402,18 +402,23 @@ void LayoutBoxModelObject::setBackingNeedsPaintInvalidationInRect(const LayoutRe
     }
 }
 
-void LayoutBoxModelObject::invalidateDisplayItemClientOnBacking(const DisplayItemClientWrapper& displayItemClient, PaintInvalidationReason invalidationReason, const LayoutRect& previousPaintInvalidationRect, const LayoutRect& newPaintInvalidationRect) const
+void LayoutBoxModelObject::invalidateDisplayItemClientOnBacking(const DisplayItemClientWrapper& displayItemClient, PaintInvalidationReason invalidationReason, const Vector<LayoutRect>& paintInvalidationRects) const
 {
     if (layer()->groupedMapping()) {
-        if (GraphicsLayer* squashingLayer = layer()->groupedMapping()->squashingLayer())
-            squashingLayer->invalidateDisplayItemClient(displayItemClient, invalidationReason, enclosingIntRect(previousPaintInvalidationRect), enclosingIntRect(newPaintInvalidationRect));
+        if (GraphicsLayer* squashingLayer = layer()->groupedMapping()->squashingLayer()) {
+            // Note: the subpixel accumulation of layer() does not need to be added here. It is already taken into account.
+            Vector<IntRect> layerPaintInvalidationRects;
+            for (const auto& rect : paintInvalidationRects)
+                layerPaintInvalidationRects.append(enclosingIntRect(rect));
+            squashingLayer->invalidateDisplayItemClient(displayItemClient, invalidationReason, layerPaintInvalidationRects);
+        }
     } else if (CompositedLayerMapping* compositedLayerMapping = layer()->compositedLayerMapping()) {
         if (this->displayItemClient() != displayItemClient.displayItemClient() && isBox() && toLayoutBox(this)->usesCompositedScrolling()) {
             // This paint invalidation container is using composited scrolling, and we are invalidating a scrolling content,
             // so we should invalidate on the scrolling contents layer only.
-            compositedLayerMapping->invalidateDisplayItemClientOnScrollingContentsLayer(displayItemClient, invalidationReason, previousPaintInvalidationRect, newPaintInvalidationRect);
+            compositedLayerMapping->invalidateDisplayItemClientOnScrollingContentsLayer(displayItemClient, invalidationReason, paintInvalidationRects);
         } else {
-            compositedLayerMapping->invalidateDisplayItemClient(displayItemClient, invalidationReason, previousPaintInvalidationRect, newPaintInvalidationRect);
+            compositedLayerMapping->invalidateDisplayItemClient(displayItemClient, invalidationReason, paintInvalidationRects);
         }
     }
 }