fix packages for latest SDK changes

pkg/observe/test/observe_test_utils.dart

Index: pkg/observe/test/observe_test_utils.dart
diff --git a/pkg/observe/test/observe_test_utils.dart b/pkg/observe/test/observe_test_utils.dart
index 2d4e7cbf63af2cf0de0cc797a7ecfccc39e66bf2..fe3e8694635cb69f5a8e717a3fd2037245adf47c 100644
--- a/pkg/observe/test/observe_test_utils.dart
+++ b/pkg/observe/test/observe_test_utils.dart
@@ -8,57 +8,15 @@ import 'dart:async';
 import 'package:observe/observe.dart';
 import 'package:unittest/unittest.dart';
 
+import 'package:observe/src/microtask.dart';
+export 'package:observe/src/microtask.dart';
+
 // TODO(jmesserly): use matchers when we have a way to compare ChangeRecords.
 // For now just use the toString.
 expectChanges(actual, expected, {reason}) =>
     expect('$actual', '$expected', reason: reason);
 
 /**
- * This change pumps events relevant to observers and data-binding tests.
- * This must be used inside an [observeTest].
- *
- * Executes all pending [runAsync] calls on the event loop, as well as
- * performing [Observable.dirtyCheck], until there are no more pending events.
- * It will always dirty check at least once.
- */
-void performMicrotaskCheckpoint() {
-  Observable.dirtyCheck();
-
-  while (_pending.length > 0) {
-    var pending = _pending;
-    _pending = [];
-
-    for (var callback in pending) {
-      try {
-        callback();
-      } catch (e, s) {
-        new Completer().completeError(e, s);
-      }
-    }
-
-    Observable.dirtyCheck();
-  }
-}
-
-List<Function> _pending = [];
-
-/**
- * Wraps the [testCase] in a zone that supports [performMicrotaskCheckpoint],
- * and returns the test case.
- */
-wrapMicrotask(void testCase()) {
-  return () {
-    runZonedExperimental(() {
-      try {
-        testCase();
-      } finally {
-        performMicrotaskCheckpoint();
-      }
-    }, onRunAsync: (callback) => _pending.add(callback));
-  };
-}
-
-/**
  * This is a special kind of unit [test], that supports
  * calling [performMicrotaskCheckpoint] during the test to pump events
  * that original from observable objects.