[CSS Shapes] shape-margin in percentage units always computes to 0px

Source/core/rendering/shapes/ShapeOutsideInfo.cpp

Index: Source/core/rendering/shapes/ShapeOutsideInfo.cpp
diff --git a/Source/core/rendering/shapes/ShapeOutsideInfo.cpp b/Source/core/rendering/shapes/ShapeOutsideInfo.cpp
index ed3beb1933a8a4bbd2ab21571e50b4f69481aba4..6b4138b66064792b7e32429ee8adf85d9171312b 100644
--- a/Source/core/rendering/shapes/ShapeOutsideInfo.cpp
+++ b/Source/core/rendering/shapes/ShapeOutsideInfo.cpp
@@ -34,6 +34,7 @@
 #include "core/rendering/RenderBlockFlow.h"
 #include "core/rendering/RenderBox.h"
 #include "core/rendering/RenderImage.h"
+#include "platform/LengthFunctions.h"
 
 namespace WebCore {
 
@@ -123,7 +124,9 @@ const Shape& ShapeOutsideInfo::computedShape() const
     const RenderStyle& containingBlockStyle = *m_renderer.containingBlock()->style();
 
     WritingMode writingMode = containingBlockStyle.writingMode();
-    Length margin = style.shapeMargin();
+    LayoutUnit maximumValue = m_renderer.containingBlock() ? m_renderer.containingBlock()->contentWidth() : LayoutUnit();
+    float margin = floatValueForLength(m_renderer.style()->shapeMargin(), maximumValue.toFloat());
+
     float shapeImageThreshold = style.shapeImageThreshold();
     ASSERT(style.shapeOutside());
     const ShapeValue& shapeValue = *style.shapeOutside();