servo: Merge #16428 - layout: Floor to 0 when computing intrinsic sizes with box-sizing:border-box (from stshine:box-sizing); r=emilio

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Improves bitbucket.

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Source-Repo: https://github.com/servo/servo
Source-Revision: 349ddb555a8be9daad691a201f72682a141e34e4

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : cb58ba765ba8e7add9138c25dd448d9657c4e847

servo/components/layout/fragment.rs

@@ -937,7 +937,7 @@ impl Fragment {
             }
 
             if self.style.get_position().box_sizing == box_sizing::T::border_box {
-                specified -= border_padding
+                specified = max(Au(0), specified - border_padding);
             }
         }