Add ClearanceOffset to LayoutNG Constraint space.

third_party/WebKit/Source/core/layout/ng/ng_units.h

Index: third_party/WebKit/Source/core/layout/ng/ng_units.h
diff --git a/third_party/WebKit/Source/core/layout/ng/ng_units.h b/third_party/WebKit/Source/core/layout/ng/ng_units.h
index cc2dd519e79b0b39d596cef20880d906a27c1e7a..c3ed32c33923d56989b6bb05d777c7c449640ec7 100644
--- a/third_party/WebKit/Source/core/layout/ng/ng_units.h
+++ b/third_party/WebKit/Source/core/layout/ng/ng_units.h
@@ -120,6 +120,11 @@ struct CORE_EXPORT NGPhysicalOffset {
   }
 };
 
+CORE_EXPORT inline std::ostream& operator<<(std::ostream& os,
+                                            const NGPhysicalOffset& value) {
+  return os << value.ToString();
+}
+
 struct CORE_EXPORT NGPhysicalSize {
   NGPhysicalSize() {}
   NGPhysicalSize(LayoutUnit width, LayoutUnit height)