Added 1.13 changelog entries for changes in dart:async

CHANGELOG.md

 ## 1.14.0
 
 ### Core library changes
 * `dart:math`
   * `Random` added a `secure` constructor returning a cryptographically secure
     random generator which reads from the entropy source provided by the
     embedder for every generated random value.
 
 ## 1.13.0
 
 ### Core library changes
 * `dart:async`
+  * `StreamController` added getters for `onListen`, `onPause`, and `onResume`
+    with the corresponding new `typedef void ControllerCallback()`.
+  * `StreamController` added a getter for `onCancel` with the corresponding
+    new `typedef ControllerCancelCallback()`;
   * `StreamTransformer` instances created with `fromHandlers` with no
     `handleError` callback now forward stack traces along with errors to the
     resulting streams.
 
 * `dart:core`
   * `Uri` added `removeFragment` method.
   * `String.allMatches` (implementing `Pattern.allMatches`) is now lazy,
     as all `allMatches` implementations are intended to be.
   * `Resource` is deprecated in favor of the resource package.
     See https://pub.dartlang.org/packages/resource to learn more. This is
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     they will keep the Dart process alive until they time out. This fixes the
     handling of persistent connections. Previously, the client would shut down
     immediately after a request.
 
   * **Breaking change:** `HttpServer` no longer compresses all traffic by
     default. The new `autoCompress` property can be set to `true` to re-enable
     compression.
 
 * `dart:isolate`: `Isolate.spawnUri` added the optional `packageRoot` argument,
   which controls how it resolves `package:` URIs.