docs(API): 翻译完了 AsyncPipe

aio/content/translations/cn/api-plan.md

@@ -41,7 +41,7 @@
 [x]  | forms/NgForm  | 0.50
 [ ]  | core/Renderer2  | 0.49
 [x]  | core/HostListener  | 0.47
-[ ]  | common/AsyncPipe  | 0.45
+[x]  | common/AsyncPipe  | 0.45
 [ ]  | core/ViewContainerRef  | 0.42
 [ ]  | common/NgTemplateOutlet  | 0.42
 [ ]  | common/Location  | 0.41

packages/common/src/pipes/async_pipe.ts

@@ -46,22 +46,32 @@ const _observableStrategy = new ObservableStrategy();
  *
  * Unwraps a value from an asynchronous primitive.
  *
+ * 从一个异步回执中解出一个值。
+ *
  * The `async` pipe subscribes to an `Observable` or `Promise` and returns the latest value it has
  * emitted. When a new value is emitted, the `async` pipe marks the component to be checked for
  * changes. When the component gets destroyed, the `async` pipe unsubscribes automatically to avoid
  * potential memory leaks.
  *
+ * `async` 管道会订阅一个 `Observable` 或 `Promise`，并返回它发出的最近一个值。
+ * 当新值到来时，`async` 管道就会把该组件标记为需要进行变更检测。当组件被销毁时，`async` 管道就会自动取消订阅，以消除潜在的内存泄露问题。
  *
  * ## Examples
  *
+ * ## 例子
+ *
  * This example binds a `Promise` to the view. Clicking the `Resolve` button resolves the
  * promise.
  *
+ * 这个例子把一个 `Promise` 绑定到了视图中。点击 `Resolve` 按钮就会解析此 Promise。
+ *
  * {@example common/pipes/ts/async_pipe.ts region='AsyncPipePromise'}
  *
  * It's also possible to use `async` with Observables. The example below binds the `time` Observable
  * to the view. The Observable continuously updates the view with the current time.
  *
+ * 还可以把 `async` 用于 `Observable`。下面的例子就把 `time` 这个 `Observable` 绑定到了视图上。这个 `Observable` 会不断使用当前时间更新视图。
+ *
  * {@example common/pipes/ts/async_pipe.ts region='AsyncPipeObservable'}
  *
  *