[Edit] Implement model cache

Implement a cache to store domain object models,
to allow the cache for individual objects to distinguish
objects based on their parentage and avoid ambiguous
Remove actions (WTD-473.)

platform/commonUI/edit/src/objects/EditableModelCache.js

@@ -0,0 +1,42 @@
+/*global define*/
+
+define(
+    [],
+    function () {
+        "use strict";
+
+        /**
+         * An editable model cache stores domain object models that have been
+         * made editable, to support a group that can be saved all-at-once.
+         * This is useful in Edit mode, which is launched for a specific
+         * object but may contain changes across many objects.
+         * @constructor
+         */
+        function EditableModelCache() {
+            var cache = {};
+
+            // Deep-copy a model. Models are JSONifiable, so this can be
+            // done by stringification then destringification
+            function clone(model) {
+                return JSON.parse(JSON.stringify(model));
+            }
+
+            return {
+                /**
+                 * Get this domain object's model from the cache (or
+                 * place it in the cache if it isn't in the cache yet)
+                 * @returns a clone of the domain object's model
+                 */
+                getCachedModel: function (domainObject) {
+                    var id = domainObject.getId();
+
+                    return (cache[id] =
+                        cache[id] || clone(domainObject.getModel()));
+                }
+            };
+
+        }
+
+        return EditableModelCache;
+    }
+);