Relayout an object that becomes a spanner.

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

Index: third_party/WebKit/Source/core/layout/LayoutMultiColumnSpannerPlaceholder.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutMultiColumnSpannerPlaceholder.cpp b/third_party/WebKit/Source/core/layout/LayoutMultiColumnSpannerPlaceholder.cpp
index 7b46b2a1437550e09aedeb9fd728519d2d437a13..825e40158bd460e292e181f95895260541f3111b 100644
--- a/third_party/WebKit/Source/core/layout/LayoutMultiColumnSpannerPlaceholder.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutMultiColumnSpannerPlaceholder.cpp
@@ -59,6 +59,14 @@ void LayoutMultiColumnSpannerPlaceholder::updateMarginProperties()
     setStyle(newStyle);
 }
 
+void LayoutMultiColumnSpannerPlaceholder::insertedIntoTree()
+{
+    LayoutBox::insertedIntoTree();
+    // The object may previously have been laid out as a non-spanner, but since it's a spanner now,
+    // it needs to be relaid out.
+    m_layoutObjectInFlowThread->setNeedsLayoutAndPrefWidthsRecalc(LayoutInvalidationReason::ColumnsChanged);
+}
+
 void LayoutMultiColumnSpannerPlaceholder::willBeRemovedFromTree()
 {
     if (m_layoutObjectInFlowThread) {