[Forms] Implement DialogButtonController

Implement controller for dialog buttons sufficient to satisfy
spec; these will be used to launch dialogs to collect user input
for Image Properties et al to complete toolbar for Fixed Position
view, WTD-881.

platform/forms/src/controllers/DialogButtonController.js

@@ -0,0 +1,72 @@
+/*global define*/
+define(
+    [],
+    function () {
+        'use strict';
+
+        /**
+         * Controller for the `dialog-button` control type. Provides
+         * structure for a button (embedded via the template) which
+         * will show a dialog for editing a single property when clicked.
+         * @constructor
+         * @param $scope the control's Angular scope
+         * @param {DialogService} dialogService service to use to prompt
+         *        for user input
+         */
+        function DialogButtonController($scope, dialogService) {
+            var buttonStructure,
+                buttonForm,
+                field;
+
+            // Store the result of user input to the model
+            function storeResult(result) {
+                $scope.ngModel[$scope.field] = result[$scope.field];
+            }
+
+            // Prompt for user input
+            function showDialog() {
+                dialogService.getUserInput(buttonForm, $scope.ngModel)
+                    .then(storeResult);
+            }
+
+            // Refresh state based on structure for this control
+            function refreshStructure(structure) {
+                var row = Object.create(structure.dialog || {});
+
+                structure = structure || {};
+
+                // Add the key, to read back from that row
+                row.key = $scope.field;
+
+                // Prepare the structure for the button itself
+                buttonStructure = {};
+                buttonStructure.glyph = structure.glyph;
+                buttonStructure.name = structure.name;
+                buttonStructure.description = structure.description;
+                buttonStructure.click = showDialog;
+
+                // Prepare the form; a single row
+                buttonForm = {
+                    name: structure.title,
+                    sections: [ { rows: [ row ] } ]
+                };
+            }
+
+            $scope.$watch('structure', refreshStructure);
+
+            return {
+                /**
+                 * Get the structure for an `mct-control` of type
+                 * `button`; a dialog will be launched when this button
+                 * is clicked.
+                 * @returns dialog structure
+                 */
+                getButtonStructure: function () {
+                    return buttonStructure;
+                }
+            };
+        }
+
+        return DialogButtonController;
+    }
+);