Support margin-top for legend in fieldset.

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006 Apple Computer, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 156 matching lines @@
     }
 
     setLogicalLeftForChild(*legend, logicalLeft);
 
     LayoutUnit fieldsetBorderBefore = LayoutUnit(borderBefore());
     LayoutUnit legendLogicalHeight = logicalHeightForChild(*legend);
 
     LayoutUnit legendLogicalTop;
     LayoutUnit collapsedLegendExtent;
     LayoutUnit innerBlockPadding;
-    // FIXME: We need to account for the legend's margin before too.
-    if (fieldsetBorderBefore > legendLogicalHeight) {
-      // The <legend> is smaller than the associated fieldset before border
-      // so the latter determines positioning of the <legend>. The sizing
-      // depends on the legend's margins as we want to still follow the
-      // author's cues.
-      // Firefox completely ignores the margins in this case which seems wrong.
+
+    if (legendLogicalHeight < fieldsetBorderBefore) {
+      // Center legend in fieldset border
       legendLogicalTop = (fieldsetBorderBefore - legendLogicalHeight) / 2;
-      collapsedLegendExtent = max<LayoutUnit>(
-          fieldsetBorderBefore, legendLogicalTop + legendLogicalHeight +
-                                    marginAfterForChild(*legend));
-      innerBlockPadding = marginAfterForChild(*legend)
-                              ? marginAfterForChild(*legend) - legendLogicalTop
-                              : LayoutUnit();
-    } else {
-      collapsedLegendExtent =
-          legendLogicalHeight + marginAfterForChild(*legend);
-      innerBlockPadding =
-          legendLogicalHeight - borderAfter() + marginAfterForChild(*legend);
     }
 
+    // Calculate how much legend + bottom margin sticks below the fieldset
+    // border
+    innerBlockPadding = (legendLogicalTop + legendLogicalHeight +
+                         marginAfterForChild(*legend) - fieldsetBorderBefore)
+                            .clampNegativeToZero();
+
+    if (legendLogicalTop < marginBeforeForChild(*legend)) {
+      // legend margin pushes everything down
+      innerBlockPadding += marginBeforeForChild(*legend) - legendLogicalTop;
+      legendLogicalTop = marginBeforeForChild(*legend);
+    }
+
+    collapsedLegendExtent =
+        std::max(fieldsetBorderBefore, marginBeforeForChild(*legend) +
+                                           legendLogicalHeight +
+                                           marginAfterForChild(*legend));
+
     if (m_innerBlock)
       setInnerBlockPadding(isHorizontalWritingMode(), m_innerBlock,
                            innerBlockPadding);
     setLogicalTopForChild(*legend, legendLogicalTop);
     setLogicalHeight(paddingBefore() + collapsedLegendExtent);
 
     if (legend->frameRect() != oldLegendFrameRect) {
       // We need to invalidate the fieldset border if the legend's frame
       // changed.
       setShouldDoFullPaintInvalidation();
@@ skipping 88 matching lines @@
     LayoutFlexibleBox::removeChild(oldChild);
     m_innerBlock = nullptr;
   } else if (oldChild->parent() == this) {
     LayoutFlexibleBox::removeChild(oldChild);
   } else if (m_innerBlock) {
     m_innerBlock->removeChild(oldChild);
   }
 }
 
 }  // namespace blink