Use an AbortController instead of signaling abort on AbortSignal

 - Replace WritableStreamDefaultController's [[signal]] with
   [[AbortController]], using the controller's signal where [[signal]]
   was used. Signal abort on [[abortController]] rather than the
   [[signal]].
 - Remove the note about specs not signaling abort on the
   WritableStream's signal, since this won't be possible once
   AbortSignal's "signal abort" no longer exported.

Author: shaseley

index.bs

@@ -4445,6 +4445,10 @@ the following table:
    <td><dfn>\[[abortAlgorithm]]</dfn>
    <td class="non-normative">A promise-returning algorithm, taking one argument (the abort reason),
    which communicates a requested abort to the [=underlying sink=]
+  <tr>
+   <td><dfn>\[[abortController]]</dfn>
+   <td class="non-normative">An {{AbortController}} that can be used to abort the pending write or
+   close operation when the stream is [=abort a writable stream|aborted=].
   <tr>
    <td><dfn>\[[closeAlgorithm]]</dfn>
    <td class="non-normative">A promise-returning algorithm which communicates a requested close to
@@ -4456,10 +4460,6 @@ the following table:
    <td><dfn>\[[queueTotalSize]]</dfn>
    <td class="non-normative">The total size of all the chunks stored in
    [=WritableStreamDefaultController/[[queue]]=] (see [[#queue-with-sizes]])
-  <tr>
-   <td><dfn>\[[signal]]</dfn>
-   <td class="non-normative">An {{AbortSignal}} that can be used to abort the pending write or
-   close operation when the stream is [=abort a writable stream|aborted=].
   <tr>
    <td><dfn>\[[started]]</dfn>
    <td class="non-normative">A boolean flag indicating whether the [=underlying sink=] has finished
@@ -4508,7 +4508,8 @@ closed. It is only used internally, and is never exposed to web developers.
  The <dfn id="ws-default-controller-signal" attribute
  for="WritableStreamDefaultController">signal</dfn> getter steps are:
 
- 1. Return [=this=].[=WritableStreamDefaultController/[[signal]]=].
+ 1. Return [=this=].[=WritableStreamDefaultController/[[abortController]]=]'s
+    [=AbortController/signal=].
 </div>
 
 <div algorithm>
@@ -4654,13 +4655,13 @@ The following abstract operations operate on {{WritableStream}} instances at a h
 
  1. If |stream|.[=WritableStream/[[state]]=] is "`closed`" or "`errored`", return
     [=a promise resolved with=] undefined.
- 1. [=Signal abort=] on
-    |stream|.[=WritableStream/[[controller]]=].[=WritableStreamDefaultController/[[signal]]=] with
-    |reason|.
+ 1. [=AbortController/Signal abort=] on
+    |stream|.[=WritableStream/[[controller]]=].[=WritableStreamDefaultController/[[abortController]]=]
+    with |reason|.
  1. Let |state| be |stream|.[=WritableStream/[[state]]=].
  1. If |state| is "`closed`" or "`errored`", return [=a promise resolved with=] undefined.
-    <p class="note">We re-check the state because [=signaling abort=] runs author code and that might
-    have changed the state.
+    <p class="note">We re-check the state because [=AbortController/signaling abort=] runs author
+    code and that might have changed the state.
  1. If |stream|.[=WritableStream/[[pendingAbortRequest]]=] is not undefined, return
     |stream|.[=WritableStream/[[pendingAbortRequest]]=]'s [=pending abort request/promise=].
  1. Assert: |state| is "`writable`" or "`erroring`".
@@ -5084,7 +5085,8 @@ The following abstract operations support the implementation of the
  1. Set |controller|.[=WritableStreamDefaultController/[[stream]]=] to |stream|.
  1. Set |stream|.[=WritableStream/[[controller]]=] to |controller|.
  1. Perform ! [$ResetQueue$](|controller|).
- 1. Set |controller|.[=WritableStreamDefaultController/[[signal]]=] to a new {{AbortSignal}}.
+ 1. Set |controller|.[=WritableStreamDefaultController/[[abortController]]=] to a new
+    {{AbortController}}.
  1. Set |controller|.[=WritableStreamDefaultController/[[started]]=] to false.
  1. Set |controller|.[=WritableStreamDefaultController/[[strategySizeAlgorithm]]=] to
     |sizeAlgorithm|.
@@ -6996,11 +6998,10 @@ above [=WritableStream/set up=] algorithm:
 [$WritableStreamDefaultControllerErrorIfNeeded$](|stream|.[=WritableStream/[[controller]]=], |e|).
 
 <p>The <dfn export for="WritableStream">signal</dfn> of a {{WritableStream}} |stream| is
-|stream|.[=WritableStream/[[controller]]=].[=WritableStreamDefaultController/[[signal]]=].
-Specifications can [=AbortSignal/add=] or [=AbortSignal/remove=] algorithms to this
-{{AbortSignal}}, or consult whether it is [=AbortSignal/aborted=] and its [=AbortSignal/abort
-reason=]. Specifications must not [=AbortSignal/signal abort=], as that would interfere with the
-normal use of this signal to respond to the stream being [=abort a writable stream|aborted=].
+|stream|.[=WritableStream/[[controller]]=].[=WritableStreamDefaultController/[[abortController]]=]'s
+[=AbortController/signal=]. Specifications can [=AbortSignal/add=] or [=AbortSignal/remove=]
+algorithms to this {{AbortSignal}}, or consult whether it is [=AbortSignal/aborted=] and its
+[=AbortSignal/abort reason=].
 
 <p class="note">The usual usage is, after [=WritableStream/setting up=] the {{WritableStream}},
 [=AbortSignal/add=] an algorithm to its [=WritableStream/signal=], which aborts any ongoing write