Support margin-top for legend in fieldset.

third_party/WebKit/Source/core/paint/FieldsetPainter.cpp

Index: third_party/WebKit/Source/core/paint/FieldsetPainter.cpp
diff --git a/third_party/WebKit/Source/core/paint/FieldsetPainter.cpp b/third_party/WebKit/Source/core/paint/FieldsetPainter.cpp
index f79bfb0465f27105de816db4273be2a7503ae097..26162b3839fb48c4f6394b71c141a806ac254871 100644
--- a/third_party/WebKit/Source/core/paint/FieldsetPainter.cpp
+++ b/third_party/WebKit/Source/core/paint/FieldsetPainter.cpp
@@ -31,16 +31,18 @@ void FieldsetPainter::paintBoxDecorationBackground(
   // https://bugs.webkit.org/show_bug.cgi?id=47236
   if (m_layoutFieldset.style()->isHorizontalWritingMode()) {
     LayoutUnit yOff =
-        (legend->location().y() > 0)
-            ? LayoutUnit()
-            : (legend->size().height() - m_layoutFieldset.borderTop()) / 2;
+        (legend->location().y() +
+         (legend->size().height() - m_layoutFieldset.borderTop()) / 2)
+            .clampNegativeToZero();
+
     paintRect.setHeight(paintRect.height() - yOff);
     paintRect.setY(paintRect.y() + yOff);
   } else {
     LayoutUnit xOff =
-        (legend->location().x() > 0)
-            ? LayoutUnit()
-            : (legend->size().width() - m_layoutFieldset.borderLeft()) / 2;
+        (legend->location().x() +
+         (legend->size().width() - m_layoutFieldset.borderLeft()) / 2)
+            .clampNegativeToZero();
+
     paintRect.setWidth(paintRect.width() - xOff);
     paintRect.setX(paintRect.x() + xOff);
   }
@@ -111,16 +113,18 @@ void FieldsetPainter::paintMask(const PaintInfo& paintInfo,
   // https://bugs.webkit.org/show_bug.cgi?id=47236
   if (m_layoutFieldset.style()->isHorizontalWritingMode()) {
     LayoutUnit yOff =
-        (legend->location().y() > LayoutUnit())
-            ? LayoutUnit()
-            : (legend->size().height() - m_layoutFieldset.borderTop()) / 2;
+        (legend->location().y() +
+         (legend->size().height() - m_layoutFieldset.borderTop()) / 2)
+            .clampNegativeToZero();
+
     paintRect.expand(LayoutUnit(), -yOff);
     paintRect.move(LayoutUnit(), yOff);
   } else {
     LayoutUnit xOff =
-        (legend->location().x() > LayoutUnit())
-            ? LayoutUnit()
-            : (legend->size().width() - m_layoutFieldset.borderLeft()) / 2;
+        (legend->location().x() +
+         (legend->size().width() - m_layoutFieldset.borderLeft()) / 2)
+            .clampNegativeToZero();
+
     paintRect.expand(-xOff, LayoutUnit());
     paintRect.move(xOff, LayoutUnit());
   }