Rename StreamGroup to GroupedEvents.

tests/lib/async/stream_group_by_test.dart

 // Copyright (c) 2017, 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.
 
 library stream_group_by_test;
 
 import "dart:async";
 
 import "package:expect/expect.dart";
 import "package:async_helper/async_helper.dart";
 
 int len(x) => x.length;
 String wrap(x) => "[$x]";
 
 void main() {
   asyncStart();
   // groupBy.
   test("splits", () async {
     var grouped = stringStream.groupBy<int>(len);
     var byLength = <int, Future<List<String>>>{};
-    await for (StreamGroup<int, String> group in grouped) {
+    await for (GroupedEvents<int, String> group in grouped) {
       byLength[group.key] = group.values.toList();
     }
     Expect.listEquals([1, 2, 4, 3], byLength.keys.toList());
     expectCompletes(byLength[1], ["a", "b"]);
     expectCompletes(byLength[2], ["ab"]);
     expectCompletes(byLength[3], ["abe", "lea"]);
     expectCompletes(byLength[4], ["abel", "bell", "able", "abba"]);
   });
 
   test("empty", () async {
     var grouped = emptyStream.groupBy<int>(len);
     var byLength = <int, Future<List<String>>>{};
-    await for (StreamGroup<int, String> group in grouped) {
+    await for (GroupedEvents<int, String> group in grouped) {
       byLength[group.key] = group.values.toList();
     }
     Expect.isTrue(byLength.isEmpty);
   });
 
   test("single group", () async {
     var grouped = repeatStream(5, "x").groupBy<int>(len);
     var byLength = <int, Future<List<String>>>{};
-    await for (StreamGroup<int, String> group in grouped) {
+    await for (GroupedEvents<int, String> group in grouped) {
       byLength[group.key] = group.values.toList();
     }
     Expect.listEquals([1], byLength.keys.toList());
     expectCompletes(byLength[1], ["x", "x", "x", "x", "x"]);
   });
 
   test("with error", () async {
     var grouped = stringErrorStream(3).groupBy<int>(len);
     var byLength = <int, Future<List<String>>>{};
     bool caught = false;
     try {
-      await for (StreamGroup<int, String> group in grouped) {
+      await for (GroupedEvents<int, String> group in grouped) {
         byLength[group.key] = group.values.toList();
       }
     } catch (e) {
       Expect.equals("BAD", e);
       caught = true;
     }
     Expect.isTrue(caught);
     Expect.listEquals([1, 2, 4], byLength.keys.toList());
     expectCompletes(byLength[1], ["a", "b"]);
     expectCompletes(byLength[2], ["ab"]);
@@ skipping 244 matching lines @@
     yield start++;
   }
 }
 
 Stream timerStream(int count, Duration interval) async* {
   for (int i = 0; i < count; i++) {
     await new Future.delayed(interval);
     yield i;
   }
 }