[Timeline] Allow linking during edit

...in cases where it is safe to do so (specifically, when the
linked-to object has already been persisted.)

platform/commonUI/edit/bundle.js

@@ -34,6 +34,7 @@ define([
     "./src/actions/SaveAction",
     "./src/actions/CancelAction",
     "./src/policies/EditActionPolicy",
+    "./src/policies/EditableLinkPolicy",
     "./src/policies/EditableMovePolicy",
     "./src/policies/EditNavigationPolicy",
     "./src/representers/EditRepresenter",
@@ -57,6 +58,7 @@ define([
     SaveAction,
     CancelAction,
     EditActionPolicy,
+    EditableLinkPolicy,
     EditableMovePolicy,
     EditNavigationPolicy,
     EditRepresenter,
@@ -193,6 +195,10 @@ define([
                     "category": "action",
                     "implementation": EditableMovePolicy
                 },
+                {
+                    "category": "action",
+                    "implementation": EditableLinkPolicy
+                },
                 {
                     "category": "navigation",
                     "message": "There are unsaved changes.",

platform/commonUI/edit/src/policies/EditableLinkPolicy.js

@@ -0,0 +1,52 @@
+/*****************************************************************************
+ * Open MCT Web, Copyright (c) 2014-2015, United States Government
+ * as represented by the Administrator of the National Aeronautics and Space
+ * Administration. All rights reserved.
+ *
+ * Open MCT Web is licensed under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * http://www.apache.org/licenses/LICENSE-2.0.
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ * Open MCT Web includes source code licensed under additional open source
+ * licenses. See the Open Source Licenses file (LICENSES.md) included with
+ * this source code distribution or the Licensing information page available
+ * at runtime from the About dialog for additional information.
+ *****************************************************************************/
+/*global define*/
+
+define([], function () {
+    "use strict";
+
+    /**
+     * Policy suppressing links when the linked-to domain object is in
+     * edit mode. Domain objects being edited may not have been persisted,
+     * so creating links to these can result in inconsistent state.
+     *
+     * @memberof platform/commonUI/edit
+     * @constructor
+     * @implements {Policy.<View, DomainObject>}
+     */
+    function EditableLinkPolicy() {
+    }
+
+    EditableLinkPolicy.prototype.allow = function (action, context) {
+        var key = action.getMetadata().key;
+
+        if (key === 'link') {
+            return !((context.selectedObject || context.domainObject)
+                .hasCapability('editor'));
+        }
+
+        // Like all policies, allow by default.
+        return true;
+    };
+
+    return EditableLinkPolicy;
+});

platform/core/src/actions/ActionCapability.js

@@ -28,7 +28,8 @@ define(
     [],
     function () {
         "use strict";
-        var DISALLOWED_ACTIONS = ["copy", "link", "window", "follow"];
+        var DISALLOWED_ACTIONS = ["copy", "window", "follow"];
+
         /**
          * The ActionCapability allows applicable Actions to be retrieved and
          * performed for specific domain objects, e.g.: