Stop expecting errors when pausing, resuming or canceling a canceled stream.

tests/html/streams_test.dart

 library streams_test;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:async';
 import 'dart:html';
 
 class StreamHelper {
   var _a;
   StreamHelper() {
     _a = new TextInputElement();
@@ skipping 69 matching lines @@
     expect(callCount, 1);
 
     subscription.cancel();
     helper.pulse();
     expect(callCount, 1);
 
     expect(() {
       subscription.onData((_) {});
     }, throws);
 
-    expect(() {
-      subscription.pause();
-    }, throws);
-
-    expect(() {
-      subscription.resume();
-    }, throws);
+    // Calling these after a cancel does nothing.
+    subscription.cancel();
+    subscription.pause();
+    subscription.resume();
   });
 
   test('pause/resume', () {
     var helper = new StreamHelper();
 
     var callCount = 0;
     var subscription = helper.stream.listen((_) {
       ++callCount;
     });
 
@@ skipping 17 matching lines @@
     subscription.pause();
     helper.pulse();
     subscription.resume();
     helper.pulse();
     expect(callCount, 2);
 
     completer.complete(0);
     helper.pulse();
     expect(callCount, 3);
 
-    // Not paused.
-    expect(() {
-      subscription.resume();
-    }, throws);
+    // Not paused, but resuming once too often is ok.
+    subscription.resume();
   });
 
   test('onData', () {
     var helper = new StreamHelper();
 
     var callCountOne = 0;
     var subscription = helper.stream.listen((_) {
       ++callCountOne;
     });
 
@@ skipping 128 matching lines @@
   });
 
   test('singleWhere', () {
     stream.singleWhere((_) => true).then((_) {});
   });
 
   test('elementAt', () {
     stream.elementAt(0).then((_) {});
   });
 }