Add mus::mojom::ChannelHandle for passing IPC::ChannelHandle via mojo IPC.

components/mus/public/interfaces/channel_handle.mojom

Index: components/mus/public/interfaces/channel_handle.mojom
diff --git a/content/test/data/web_ui_test_mojo_bindings.mojom b/components/mus/public/interfaces/channel_handle.mojom
similarity index 54%
copy from content/test/data/web_ui_test_mojo_bindings.mojom
copy to components/mus/public/interfaces/channel_handle.mojom
index c5893828dd2fbf872eb28410fc1a8c503cf9ae7d..8fbf4780cdffcf4be23db714b8326b5b43098c30 100644
--- a/content/test/data/web_ui_test_mojo_bindings.mojom
+++ b/components/mus/public/interfaces/channel_handle.mojom
@@ -2,9 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-module content.mojom;
+module mus.mojom;
 
-interface BrowserTarget {
-  Start() => ();
-  Stop();
+// import "components/mus/public/interfaces/command_buffer.mojom";
+
+struct ChannelHandle {
+  string name;
+  handle socket;
 };