docs(cupertino_http): Clarify that happens when a request is cancelled (#1834)

Author: brianquinlan

pkgs/cupertino_http/CHANGELOG.md

@@ -1,7 +1,8 @@
 ## 2.4.0-wip
 
 * Switch to `package:objective_c` `8.1.0` and `package:ffigen` `19.1.0`.
-
+* Add URL to thrown `RequestAbortedException`.
+ 
 ## 2.3.0
 
 * Add the ability to abort requests.

pkgs/cupertino_http/lib/src/cupertino_client.dart

@@ -207,14 +207,18 @@ class CupertinoClient extends BaseClient {
     // 2. The user aborts the request, which can happen at any point in the
     //    request lifecycle and causes `CupertinoClient.send` to throw
     //    a `RequestAbortedException` exception.
+    //
+    // In both of these cases [URLSessionTask.cancel] is called, which completes
+    // the task with a NSURLErrorCancelled error.
     final isCancelError =
         error?.domain.toDartString() == 'NSURLErrorDomain' &&
         error?.code == _nsurlErrorCancelled;
     if (error != null &&
         !(isCancelError && taskTracker.responseListenerCancelled)) {
       final Exception exception;
       if (isCancelError) {
-        exception = RequestAbortedException();
+        assert(taskTracker.requestAborted);
+        exception = RequestAbortedException(taskTracker.request.url);
       } else {
         exception = NSErrorClientException(error, taskTracker.request.url);
       }