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 05e083c2d1c08572ad0cde799d086cd39cd547cb..17d70e2db950bf2b44a6ff63f1cb199197b76292 100644
--- a/Source/core/rendering/RenderBox.cpp
+++ b/Source/core/rendering/RenderBox.cpp
@@ -3760,7 +3760,10 @@ static bool isReplacedElement(Node* node)
 
 bool RenderBox::avoidsFloats() const
 {
-    return isReplaced() || isReplacedElement(node()) || 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() || isReplacedElement(node()) || isHR() || isLegend() || isTable() || (!isFloatingOrOutOfFlowPositioned() && createsBlockFormattingContext());
 }
 
 PaintInvalidationReason RenderBox::paintInvalidationReason(const RenderLayerModelObject& paintInvalidationContainer,
@@ -3879,6 +3882,12 @@ void RenderBox::invalidatePaintRectClippedByOldAndNewBounds(const RenderLayerMod
         invalidatePaintUsingContainer(&paintInvalidationContainer, rectClippedByNewBounds, PaintInvalidationIncremental);
 }
 
+bool RenderBox::createsBlockFormattingContext() const
+{
+    return isInlineBlockOrInlineTable() || isFloatingOrOutOfFlowPositioned() || hasOverflowClip() || isFlexItemIncludingDeprecated()
+        || style()->specifiesColumns() || isRenderFlowThread() || isTableCell() || isTableCaption() || isFieldset() || isWritingModeRoot() || isDocumentElement() || style()->columnSpan();
+}
+
 void RenderBox::markForPaginationRelayoutIfNeeded(SubtreeLayoutScope& layoutScope)
 {
     ASSERT(!needsLayout());