add missing file

packages/react-devtools-shared/src/errors/UnknownHookError.js

@@ -0,0 +1,21 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+export default class UnknownHookError extends Error {
+  constructor(message: string) {
+    super(message);
+
+    // Maintains proper stack trace for where our error was thrown (only available on V8)
+    if (Error.captureStackTrace) {
+      Error.captureStackTrace(this, UnknownHookError);
+    }
+
+    this.name = 'UnknownHookError';
+  }
+}