Make StreamIterator not delay pausing between requests.

tests/language/language.status

 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 # This directory contains tests that are intended to show the
 # current state of the language.
 
 [ ($compiler == none || $compiler == precompiler || $compiler == dart2app || $compiler == dart2appjit) ]
 tearoff_constructor_basic_test: Skip # Crashes in checked mode -- hausner investigating
 
+# This is OK for now, but we may want to change the semantics to match the test.
+async_star_pause_test: Fail, OK
+
 # These tests are skipped in the VM because it has "--supermixin"
 # functionality enabled unconditionally.  The tests should be removed
 # once the same is true for analyzer (#24478) and dart2js (#23773)
 mixin_illegal_super_use_test: Skip # Issues 24478 and 23773
 mixin_illegal_superclass_test: Skip # Issues 24478 and 23773
 
 # These bugs refer currently ongoing language discussions.
 constructor5_test: Fail # Issue 6422
 constructor6_test: Fail # Issue 6422
 
@@ skipping 266 matching lines @@
 assert_initializer_test: SKIP  # not implemented yet, experiment is VM only.
 
 [$runtime == vm && $compiler == none && $unchecked]
 assert_initializer_test/*: MissingCompileTimeError, OK  # asserts shouldn't fail in unchecked mode.
 assert_initializer_test/none: pass
 
 [$runtime == vm && $compiler == none && $checked]
 # The VM doesn't enforce that potentially const expressions are actually
 # const expressions when the constructor is called with `const`.
 assert_initializer_test/4*: MissingCompileTimeError # Issue 392.