[css-text] inline elements should not introduce a forced line break or soft wrap opportunity

Closes w3c#3886

Author: frivoal

css-text-3/Overview.bs

@@ -2034,11 +2034,14 @@ Line Breaking Details</h3>
       not based on breaking at <a>word separators</a>)--
       and is forbidden under ''line-break: anywhere''.
 
-    <li>Out-of-flow elements do not introduce a <a>forced line break</a>
+    <li>Out-of-flow elements
+      and inline element boundaries
+      do not introduce a <a>forced line break</a>
       or <a>soft wrap opportunity</a> in the flow.
 
       <wpt>
         line-breaking/line-breaking-012.html
+        line-breaking/line-breaking-015.html
         line-breaking/line-breaking-016.html
         line-breaking/line-breaking-017.html
       </wpt>