add http_get_cache

experimental/http_get_cache/lib/src/extensions.dart

@@ -0,0 +1,26 @@
+import 'package:cachecontrol/cachecontrol.dart';
+import 'package:http/http.dart';
+
+const _cacheControlHeader = 'cache-control';
+
+extension CacheControlRequest on BaseRequest {
+  RequestCacheControl get cacheControl {
+    final raw = headers[_cacheControlHeader] ?? '';
+    return RequestCacheControl.parse(raw);
+  }
+
+  set cacheControl(RequestCacheControl value) {
+    headers[_cacheControlHeader] = value.toString();
+  }
+}
+
+extension CacheControlBaseResponse on BaseResponse {
+  ResponseCacheControl get cacheControl {
+    final raw = headers[_cacheControlHeader] ?? '';
+    return ResponseCacheControl.parse(raw);
+  }
+
+  set cacheControl(ResponseCacheControl value) {
+    headers[_cacheControlHeader] = value.toString();
+  }
+}