[Policy] Implement action decorator

Implement policy-driven action decorator, sufficient to satisfy
spec. WTD-973.

platform/policy/src/PolicyActionDecorator.js

@@ -0,0 +1,37 @@
+/*global define*/
+
+define(
+    [],
+    function () {
+        "use strict";
+
+        /**
+         * Filters out actions based on policy.
+         * @param {PolicyService} policyService the service which provides
+         *        policy decisions
+         * @param {ActionService} actionService the service to decorate
+         */
+        function PolicyActionDecorator(policyService, actionService) {
+            return {
+                /**
+                 * Get actions which are applicable in this context.
+                 * These will be filters to remove any actions which
+                 * are deemed inapplicable by policy.
+                 * @param context the context in which the action will occur
+                 * @returns {Action[]} applicable actions
+                 */
+                getActions: function (context) {
+                    // Check if an action is allowed by policy.
+                    function allow(action) {
+                        return policyService.allow('action', action, context);
+                    }
+
+                    // Look up actions, filter out the disallowed ones.
+                    return actionService.getActions(context).filter(allow);
+                }
+            };
+        }
+
+        return PolicyActionDecorator;
+    }
+);