Add Zotero.Utilities.defineProperty convenience method

Use this to create enumerable properties in object prototypes.

chrome/content/zotero/xpcom/utilities_internal.js

@@ -366,6 +366,24 @@ Zotero.Utilities.Internal = {
 				break;
 			}
 		}
+	},
+	
+	/**
+	 * Defines property on the object's prototype.
+	 * More compact way to do Object.defineProperty
+	 *
+	 * @param {Object} obj Target object
+	 * @param {String} prop Property to be defined
+	 * @param {Object} desc Propery descriptor. If not overriden, "enumerable" is true
+	 */
+	"defineProperty": function(obj, prop, desc) {
+		if (typeof prop != 'string') throw new Error("Property must be a string");
+		var d = { __proto__: null, enumerable: true }; // Enumerable by default
+		for (let p in desc) {
+			if (!desc.hasOwnProperty(p)) continue;
+			d[p] = desc[p];
+		}
+		Object.defineProperty(obj.prototype, prop, d);
 	}
 }