Support locking of directory entries

Moves the locking algorithm from file entry to file system entry.

Fixes whatwg#137

Author: Nathan Memmott

index.bs

@@ -135,8 +135,8 @@ To <dfn for="file system entry">take a lock</dfn> with a |value| of
 
 1. Let |lock| be the |entry|'s [=file system entry/lock=].
 1. Let |count| be the |entry|'s [=file system entry/shared lock count=].
-1. If |entry|  is a [=directory entry=]:
-   1. Let |descendantLockStatus| be the result of [=file system entry/lock/checking for a descendant lock=] on |entry|.
+1. If |entry| is a [=directory entry=]:
+   1. Let |descendantLockStatus| be the result of [=file system entry/checking for a descendant lock=] on |entry|.
    1. If |descendantLockStatus| is "`taken`":
      1. Return "`failure`".
 1. If |value| is "`exclusive`":
@@ -158,15 +158,15 @@ Note: These steps have to be run on the [=file system queue=].
 </div>
 
 <div algorithm>
-To <dfn for="file system entry/lock">check for a descendant lock</dfn> on a given
+To <dfn for="file system entry">check for a descendant lock</dfn> on a given
 [=directory entry=] |directory|:
 
 1. [=set/For each=] |child| of |directory|'s [=directory entry/children=]:
   1. Let |lock| be the |child|'s [=file system entry/lock=].
   1. If |lock| is not "`open`":
     1. Return "`taken`".
   1. If |child| is a [=directory entry=]:
-    1. Let |descendantLockStatus| be the result of [=file system entry/lock/checking for a descendant lock=] on |child|.
+    1. Let |descendantLockStatus| be the result of [=file system entry/checking for a descendant lock=] on |child|.
     1. If |descendantLockStatus| is "`taken`":
       1. Return "`taken`".
 1. Return "`open`".