Forward drain argument through after .take(0)

Fixes #30305

Change-Id: I7a30cee3e9a406e99f5d714a201b031c428a12e8
Reviewed-on: https://dart-review.googlesource.com/74015
Reviewed-by: Lasse R.H. Nielsen <lrn@google.com>
Commit-Queue: Lasse R.H. Nielsen <lrn@google.com>

CHANGELOG.md

@@ -21,6 +21,11 @@
     succeed.
 *   Exported `Future` and `Stream` from `dart:core`.
 
+#### `dart:async`
+
+*   Fix a bug where calling `stream.take(0).drain(value)` would not correctly
+    forward the `value` through the returned `Future`.
+
 ## 2.1.0-dev.3.0
 
 ### Core library changes

sdk/lib/async/stream_impl.dart

@@ -766,7 +766,7 @@ class _DoneStreamSubscription<T> implements StreamSubscription<T> {
   Future<E> asFuture<E>([E futureValue]) {
     _Future<E> result = new _Future<E>();
     _onDone = () {
-      result._completeWithValue(null);
+      result._completeWithValue(futureValue);
     };
     return result;
   }

tests/lib_2/async/stream_take_test.dart

@@ -61,6 +61,9 @@ tests() async {
   Expect.listEquals([], await makeStream(5).take(0).toList());
 
   Expect.listEquals([], await makeStream(0).take(0).toList());
+
+  // Regression for https://github.com/dart-lang/sdk/issues/30305
+  Expect.equals('result', await makeStream(5).take(0).drain('result'));
 }
 
 Future expectThrowsAsync(Future computation, String name) {