Re-land of issue 200623006: Set geometry dirty bits on composited layer mappings w/squashing

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 136118ad029de170fc03c93fd1f32edcb189f742..d8f2cf52947c44d089278f28f8739934e2ae48a5 100644
--- a/Source/core/rendering/compositing/CompositedLayerMapping.cpp
+++ b/Source/core/rendering/compositing/CompositedLayerMapping.cpp
@@ -176,7 +176,7 @@ CompositedLayerMapping::~CompositedLayerMapping()
     for (size_t i = 0; i < m_squashedLayers.size(); ++i) {
         RenderLayer* oldSquashedLayer = m_squashedLayers[i].renderLayer;
         if (oldSquashedLayer->groupedMapping() == this) {
-            oldSquashedLayer->setGroupedMapping(0);
+            oldSquashedLayer->setGroupedMapping(0, true);
             oldSquashedLayer->setLostGroupedMapping(true);
         }
     }