Split StyleSurroundData::margin into four individual Lengths.

third_party/WebKit/Source/platform/LengthBox.h

Index: third_party/WebKit/Source/platform/LengthBox.h
diff --git a/third_party/WebKit/Source/platform/LengthBox.h b/third_party/WebKit/Source/platform/LengthBox.h
index b5ddf2ab82ae5070ff5685dcfa69810e81653be8..f9927a7040cfab6a793b046df726c8f48910065e 100644
--- a/third_party/WebKit/Source/platform/LengthBox.h
+++ b/third_party/WebKit/Source/platform/LengthBox.h
@@ -68,6 +68,24 @@ class PLATFORM_EXPORT LengthBox {
                              const Length& bottom,
                              const Length& left,
                              const Length& right);
+  static const Length& Start(WritingMode,
+                             TextDirection,
+                             const Length& top,
+                             const Length& left,
+                             const Length& right,
+                             const Length& bottom);
+  static const Length& End(WritingMode,
+                           TextDirection,
+                           const Length& top,
+                           const Length& left,
+                           const Length& right,
+                           const Length& bottom);
+  static const Length& Over(WritingMode,
+                            const Length& top,
+                            const Length& right);
+  static const Length& Under(WritingMode,
+                             const Length& bottom,
+                             const Length& left);
 
   const Length& Left() const { return left_; }
   const Length& Right() const { return right_; }