Revert of [cast_channel] Move cast_channel related files from //extensions to //components

extensions/common/api/cast_channel/authority_keys.proto

Index: extensions/common/api/cast_channel/authority_keys.proto
diff --git a/extensions/common/api/cast_channel/authority_keys.proto b/extensions/common/api/cast_channel/authority_keys.proto
new file mode 100644
index 0000000000000000000000000000000000000000..791e831482e7332009304e29c6a7ab178ae9560b
--- /dev/null
+++ b/extensions/common/api/cast_channel/authority_keys.proto
@@ -0,0 +1,17 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+syntax = "proto2";
+
+option optimize_for = LITE_RUNTIME;
+
+package extensions.api.cast_channel.proto;
+
+message AuthorityKeys {
+  message Key {
+    required bytes fingerprint = 1;
+    required bytes public_key = 2;
+  }
+  repeated Key keys = 1;
+}