Start of adding enums for error codes

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 {
 
 struct NodeData {
   uint32 parent_id;
   uint32 node_id;
   uint32 view_id;
   mojo.Rect bounds;
   // TODO(sky): add visible.
 };
 
+enum ErrorCode {
+  ERROR_CODE_NONE,
+  ERROR_CODE_VALUE_IN_USE,
+  ERROR_CODE_ILLEGAL_ARGUMENT,
+  ERROR_CODE_UNEXPECTED_CHANGE_ID,
+};
+
 // ViewManagerInitService is responsible for launching the client that controls
 // the root node. mojo::view_manager returns an instance of this. All other
 // connections are established by the client this creates.
 interface ViewManagerInitService {
   EmbedRoot(string url) => (bool success);
 };
 
 // Functions that mutate the hierarchy take a change id. This is an ever
 // increasing integer used to identify the change. Every hierarchy change
 // increases this value. The server only accepts changes where the supplied
 // |server_change_id| matches the expected next value. This ensures changes are
 // made in a well defined order.
 //
 // Nodes and Views are identified by a uint32. The upper 16 bits are the
 // connection id, and the lower 16 the id assigned by the client.
 //
 // The root node is identified with a connection id of 0, and value of 1.
 [Client=ViewManagerClient]
 interface ViewManagerService {
   // Creates a new node with the specified id. It is up to the client to ensure
   // the id is unique to the connection (the id need not be globally unique).
   // Additionally the connection id (embedded in |node_id|) must match that of
   // the connection.
-  CreateNode(uint32 node_id) => (bool success);
+  // Errors:
+  //   ERROR_CODE_VALUE_IN_USE: a node already exists with the specified id.
+  //   ERROR_CODE_ILLEGAL_ARGUMENT: The connection part of |node_id| does not
+  //     match the connection id of the client.
+  CreateNode(uint32 node_id) => (ErrorCode error_code);
 
   // Deletes a node. This does not recurse. No hierarchy change notifications
   // are sent as a result of this. Only the connection that created the node can
   // delete it.
   DeleteNode(uint32 node_id, uint32 change_id) => (bool success);
 
   // Sets the specified bounds of the specified node.
   SetNodeBounds(uint32 node_id, mojo.Rect bounds) => (bool success);
 
   // Sets the visibility of the specified node to |visible|. Connections are
@@ skipping 146 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);
 };
 
 }