Bug 991904 - Create a way to load devtools modules lazily. r=dcamp

toolkit/devtools/Loader.jsm

@@ -275,6 +275,24 @@ DevToolsLoader.prototype = {
     return this.require.apply(this, arguments);
   },
 
+  /**
+   * Define a getter property on the given object that requires the given
+   * module. This enables delaying importing modules until the module is
+   * actually used.
+   *
+   * @param Object obj
+   *    The object to define the property on.
+   * @param String property
+   *    The property name.
+   * @param String module
+   *    The module path.
+   */
+  lazyRequireGetter: function (obj, property, module) {
+    Object.defineProperty(obj, property, {
+      get: () => this.require(module)
+    });
+  },
+
   /**
    * Add a URI to the loader.
    * @param string id

toolkit/devtools/tests/unit/head_devtools.js

@@ -4,6 +4,7 @@ const Ci = Components.interfaces;
 const Cu = Components.utils;
 const Cr = Components.results;
 
+Cu.import("resource://gre/modules/devtools/Loader.jsm");
 Cu.import("resource://gre/modules/devtools/DevToolsUtils.jsm");
 
 // Register a console listener, so console messages don't just disappear

toolkit/devtools/tests/unit/test_independent_loaders.js

@@ -1,9 +1,6 @@
 /* Any copyright is dedicated to the Public Domain.
    http://creativecommons.org/publicdomain/zero/1.0/ */
 
-const { DevToolsLoader } =
-  Cu.import("resource://gre/modules/devtools/Loader.jsm", {});
-
 /**
  * Ensure that each instance of the Dev Tools loader contains its own loader
  * instance, and also returns unique objects.  This ensures there is no sharing

toolkit/devtools/tests/unit/test_invisible_loader.js

@@ -1,8 +1,6 @@
 /* Any copyright is dedicated to the Public Domain.
    http://creativecommons.org/publicdomain/zero/1.0/ */
 
-const { DevToolsLoader } =
-  Cu.import("resource://gre/modules/devtools/Loader.jsm", {});
 Cu.import("resource://gre/modules/jsdebugger.jsm");
 addDebuggerToGlobal(this);
 

toolkit/devtools/tests/unit/test_require_lazy.js

@@ -0,0 +1,14 @@
+/* -*- Mode: js; js-indent-level: 2; -*- */
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+// Test devtools.lazyRequireGetter
+
+function run_test() {
+  const o = {};
+  devtools.lazyRequireGetter(o, "asyncUtils", "devtools/async-utils");
+  const asyncUtils = devtools.require("devtools/async-utils");
+  // XXX: do_check_eq only works on primitive types, so we have this
+  // do_check_true of an equality expression.
+  do_check_true(o.asyncUtils === asyncUtils);
+}

toolkit/devtools/tests/unit/xpcshell.ini

@@ -7,3 +7,4 @@ tail =
 [test_safeErrorString.js]
 [test_defineLazyPrototypeGetter.js]
 [test_async-utils.js]
+[test_require_lazy.js]