docs(API): 翻译完了 common/http

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

@@ -65,13 +65,13 @@
 [x]  | common/JsonPipe  | 0.25
 [x]  | forms/FormArray  | 0.25
 [x]  | common/CommonModule  | 0.24
-[ ]  | router/NavigationExtras  | 0.24
+[x]  | router/NavigationExtras  | 0.24
 [x]  | core/HostBinding  | 0.23
 [x]  | core/ContentChild  | 0.22
 [x]  | core/ViewChildren  | 0.22
 [x]  | common/http/HttpResponse  | 0.22
 [x]  | router/ActivatedRouteSnapshot  | 0.22
-[ ]  | common/http  | 0.21
+[x]  | common/http  | 0.21
 [ ]  | core/ChangeDetectorRef  | 0.21
 [ ]  | router/NavigationStart  | 0.21
 [ ]  | common/formatDate  | 0.21

packages/common/http/src/backend.ts

@@ -14,12 +14,18 @@ import {HttpEvent} from './response';
  * Transforms an `HttpRequest` into a stream of `HttpEvent`s, one of which will likely be a
  * `HttpResponse`.
  *
+ * 把一个 `HttpRequest` 转换成 `HttpEvent` 组成的流，`HttpResponse` 就是其中之一。
+ *
  * `HttpHandler` is injectable. When injected, the handler instance dispatches requests to the
  * first interceptor in the chain, which dispatches to the second, etc, eventually reaching the
  * `HttpBackend`.
  *
+ * `HttpHandler` 是可注入的。当被注入时，该处理器的实例会把请求派发给拦截器链中的第一个拦截器，第一个拦截器会再派发给第二个拦截器，以此类推。
+ * 最终抵达 `HttpBackend`。
+ *
  * In an `HttpInterceptor`, the `HttpHandler` parameter is the next interceptor in the chain.
  *
+ * 在 `HttpInterceptor` 中，`HttpHandler` 参数就表示链中的下一个拦截器。
  *
  */
 export abstract class HttpHandler {
@@ -29,11 +35,16 @@ export abstract class HttpHandler {
 /**
  * A final `HttpHandler` which will dispatch the request via browser HTTP APIs to a backend.
  *
+ * 最后一个 `HttpHandler`，它将会把该请求通过浏览器的 HTTP API 发到后端。
+ *
  * Interceptors sit between the `HttpClient` interface and the `HttpBackend`.
  *
+ * 拦截器位于 `HttpClient` 接口和 `HttpBackend` 之间。
+ *
  * When injected, `HttpBackend` dispatches requests directly to the backend, without going
  * through the interceptor chain.
  *
+ * 当它被注入时，`HttpBackend` 会把请求直接发给后端，而不会经过拦截器链。
  *
  */
 export abstract class HttpBackend implements HttpHandler {