Refactor avoidsFloats() to reflect CSS2.1 spec more clearly

Source/core/rendering/RenderBox.cpp

Index: Source/core/rendering/RenderBox.cpp
diff --git a/Source/core/rendering/RenderBox.cpp b/Source/core/rendering/RenderBox.cpp
index e94dcbda4058536940c8441f283bce4c019f7ec4..5d01a23a640f4cc49921b5bc55e9a5ee23468ac5 100644
--- a/Source/core/rendering/RenderBox.cpp
+++ b/Source/core/rendering/RenderBox.cpp
@@ -4078,7 +4078,16 @@ bool RenderBox::shrinkToAvoidFloats() const
 
 bool RenderBox::avoidsFloats() const
 {
-    return isReplaced() || hasOverflowClip() || isHR() || isLegend() || isWritingModeRoot() || isFlexItemIncludingDeprecated();
+    // CSS2.1: "The border box of a table, a block-level replaced element, or an element in the normal flow that establishes a new block formatting
+    // context .. must not overlap the margin box of any floats in the same block formatting context."
+    // FIXME: The inclusion of horizontal rule and legend elements here isn't covered by any spec.
+    return isReplaced() || isHR() || isLegend() || isTable() || (!isFloatingOrOutOfFlowPositioned() && createsBlockFormattingContext());
+}
+
+bool RenderBox::createsBlockFormattingContext() const
+{
+    return isInlineBlockOrInlineTable() || isFloatingOrOutOfFlowPositioned() || hasOverflowClip() || isFlexItemIncludingDeprecated()
+        || style()->specifiesColumns() || isRenderFlowThread() || isTableCell() || isTableCaption() || isFieldset() || isWritingModeRoot() || isDocumentElement() || style()->columnSpan();
 }
 
 void RenderBox::markForPaginationRelayoutIfNeeded(SubtreeLayoutScope& layoutScope)