Add helper for computing outset for 'outline'

Source/core/style/ComputedStyle.cpp

Index: Source/core/style/ComputedStyle.cpp
diff --git a/Source/core/style/ComputedStyle.cpp b/Source/core/style/ComputedStyle.cpp
index aca2e941f6a1bf3d55f75c0322887705b9ed81db..aa60c3b0eb11f65fbb038efdf99f811e6ef158c3 100644
--- a/Source/core/style/ComputedStyle.cpp
+++ b/Source/core/style/ComputedStyle.cpp
@@ -41,6 +41,7 @@
 #include "platform/fonts/Font.h"
 #include "platform/fonts/FontSelector.h"
 #include "platform/geometry/FloatRoundedRect.h"
+#include "platform/graphics/GraphicsContext.h"
 #include "wtf/MathExtras.h"
 
 #include <algorithm>
@@ -1611,6 +1612,15 @@ void ComputedStyle::resetMotionPath()
     rareNonInheritedData.access()->m_transform.access()->m_motion.m_path = nullptr;
 }
 
+int ComputedStyle::outlineOutset() const
+{
+    if (!hasOutline())
+        return 0;
+    if (outlineStyleIsAuto())
+        return GraphicsContext::focusRingOutsetExtent(outlineOffset(), outlineWidth());
+    return outlineSize();
+}
+
 bool ComputedStyle::columnRuleEquivalent(const ComputedStyle* otherStyle) const
 {
     return columnRuleStyle() == otherStyle->columnRuleStyle()