Mark when we may have been invalidated to early out on repaintTreeAfterLayout.

Source/core/rendering/RenderFlexibleBox.cpp

Index: Source/core/rendering/RenderFlexibleBox.cpp
diff --git a/Source/core/rendering/RenderFlexibleBox.cpp b/Source/core/rendering/RenderFlexibleBox.cpp
index aa4c8f483e25e359591432c1578e6f578319aa06..69c1db31ee50ea78e1290d81cd4ccfb0ee75e957 100644
--- a/Source/core/rendering/RenderFlexibleBox.cpp
+++ b/Source/core/rendering/RenderFlexibleBox.cpp
@@ -233,6 +233,8 @@ void RenderFlexibleBox::layoutBlock(bool relayoutChildren)
 
     LayoutRepainter repainter(*this, checkForRepaintDuringLayout());
 
+    setMayNeedInvalidation(true);
+
     if (updateLogicalWidthAndColumnWidth())
         relayoutChildren = true;
 
@@ -1110,6 +1112,8 @@ void RenderFlexibleBox::layoutAndPlaceChildren(LayoutUnit& crossAxisOffset, cons
             continue;
         }
 
+        child->setMayNeedInvalidation(true);
+
         LayoutUnit childPreferredSize = childSizes[i] + mainAxisBorderAndPaddingExtentForChild(child);
         setLogicalOverrideSize(child, childPreferredSize);
         if (childPreferredSize != mainAxisExtentForChild(child)) {