[Layout] Add auto-save behavior

Add an EditRepresenter which detects changes to domain
object model or view configuration and, when these
occur, triggers mutation and persistence of the domain
object. (Note that in Edit mode, 'persistence' only
flags an object as dirty; actual persistence does not
occur until the user chooses Save.)

This supports editing of position/size in Layout mode,
and the persistence of those changes. WTD-535

platform/commonUI/edit/bundle.json

@@ -89,6 +89,12 @@
                 "key": "topbar-edit",
                 "templateUrl": "templates/topbar-edit.html"
             }
+        ],
+        "representers": [
+            {
+                "implementation": "EditRepresenter.js",
+                "depends": [ "$q" ]
+            }
         ]
     }
 }

platform/commonUI/edit/src/EditRepresenter.js

@@ -0,0 +1,62 @@
+/*global define*/
+
+define(
+    [],
+    function () {
+        "use strict";
+
+        function EditRepresenter($q, scope, element, attrs) {
+            var watches = [],
+                domainObject,
+                key;
+
+            function doPersist(model) {
+                return $q.when(function () {
+                    return domainObject.useCapability("mutation", function () {
+                        return model;
+                    });
+                }).then(function (result) {
+                    return result &&
+                        domainObject.getCapability("persistence").persist();
+                });
+            }
+
+            function update() {
+                var model = scope.model,
+                    configuration = scope.configuration,
+                    key = scope.key;
+
+                if (domainObject && domainObject.hasCapability("persistence")) {
+                    model.configuration = model.configuration || {};
+                    model.configuration[key] = configuration;
+                    doPersist(model);
+                }
+            }
+
+            function destroy() {
+                // Stop watching for changes
+                watches.forEach(function (deregister) { deregister(); });
+                watches = [];
+            }
+
+            function represent(representation, representedObject) {
+                key = representation.key;
+                domainObject = representedObject;
+
+                destroy(); // Ensure existing watches are released
+
+                watches = representedObject.hasCapability("editor") ? [
+                    scope.$watch("model", update, true),
+                    scope.$watch("configuration", update, true)
+                ] : [];
+            }
+
+            return {
+                represent: represent,
+                destroy: destroy
+            };
+        }
+
+        return EditRepresenter;
+    }
+);