Makes it so a node can only the root of one connection at a time

mojo/services/public/interfaces/view_manager/view_manager.mojom

 // 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.
 
 import "mojo/services/public/interfaces/geometry/geometry.mojom"
 import "mojo/services/public/interfaces/input_events/input_events.mojom"
 import "mojo/services/public/interfaces/view_manager/view_manager_constants.mojom"
 
 module mojo.view_manager {
 
@@ skipping 109 matching lines @@
 
   // Shows the specified image (png encoded) in the specified view.
   SetViewContents(uint32 view_id,
                   handle<shared_buffer> buffer,
                   uint32 buffer_size) => (bool success);
 
   // Sets focus to the specified node.
   SetFocus(uint32 node_id) => (bool success);
 
   // Embeds the app for |url| in the specified node. More specifically this
-  // creates a new connection to the specified url, expecting to get an
+  // creates a new connection to the specified url, expecting to get a
   // ViewManagerClient and configures it with the root node |node|. Fails
   // if |node| was not created by this connection.
+  //
   // If a particular client invokes Embed() multiple times with the same url,
   // the connection is reused. When this happens the ViewManagerClient is
   // notified of the additional roots by way of OnRootAdded().
+  //
+  // A node may only be a root of one connection at a time. Subsequent calls to
+  // Embed() for the same node result in the node being removed from the
+  // current connection. The current connection is told this by way of
+  // OnNodeDeleted().
+  //
+  // This advances the server change id.
   Embed(string url, uint32 node_id) => (bool success);
 
   // TODO(sky): move these to a separate interface when FIFO works.
 
   // Sends OnViewInputEvent() to the owner of the specified view.
   DispatchOnViewInputEvent(uint32 view_id, mojo.Event event);
 };
 
 // Changes to nodes/views are not sent to the connection that originated the
 // change. For example, if connection 1 attaches a view to a node (SetView())
@@ skipping 63 matching lines @@
   //             entirely move to the window manager and this method can be
   //             removed.
   OnFocusChanged(uint32 gained_focus_id, uint32 lost_focus_id);
 
   // TODO(sky): move to separate interface when FIFO sorted out.
 
   DispatchOnViewInputEvent(uint32 view, mojo.Event event);
 };
 
 }