Bug 1504756 - [marionette] Add executeSoon() to run tasks on the main thread. r=ato

To be closer to other test harnesses which are using executeSoon()
to run a task on the main thread, this patch adds the same
method to Marionette's sync module.

Differential Revision: https://phabricator.services.mozilla.com/D13659

--HG--
extra : moz-landing-system : lando

testing/marionette/doc/internals/sync.rst

@@ -3,6 +3,8 @@ sync module
 
 Provides an assortment of synchronisation primitives.
 
+.. js:autofunction:: executeSoon
+
 .. js:autoclass:: MessageManagerDestroyedPromise
   :members:
 

testing/marionette/sync.js

@@ -18,6 +18,7 @@ const {Log} = ChromeUtils.import("chrome://marionette/content/log.js", {});
 XPCOMUtils.defineLazyGetter(this, "log", Log.get);
 
 this.EXPORTED_SYMBOLS = [
+  "executeSoon",
   "DebounceCallback",
   "IdlePromise",
   "MessageManagerDestroyedPromise",
@@ -30,6 +31,21 @@ const {TYPE_ONE_SHOT, TYPE_REPEATING_SLACK} = Ci.nsITimer;
 
 const PROMISE_TIMEOUT = AppConstants.DEBUG ? 4500 : 1500;
 
+
+/**
+ * Dispatch a function to be executed on the main thread.
+ *
+ * @param {function} func
+ *     Function to be executed.
+ */
+function executeSoon(func) {
+  if (typeof func != "function") {
+    throw new TypeError();
+  }
+
+  Services.tm.dispatchToMainThread(func);
+}
+
 /**
  * @callback Condition
  *

testing/marionette/test/unit/test_sync.js

@@ -35,6 +35,23 @@ class MockTimer {
   }
 }
 
+add_test(function test_executeSoon_callback() {
+  // executeSoon() is already defined for xpcshell in head.js. As such import
+  // our implementation into a custom namespace.
+  let sync = {};
+  ChromeUtils.import("chrome://marionette/content/sync.js", sync);
+
+  for (let func of ["foo", null, true, [], {}]) {
+    Assert.throws(() => sync.executeSoon(func), /TypeError/);
+  }
+
+  let a;
+  sync.executeSoon(() => { a = 1; });
+  executeSoon(() => equal(1, a));
+
+  run_next_test();
+});
+
 add_test(function test_PollPromise_funcTypes() {
   for (let type of ["foo", 42, null, undefined, true, [], {}]) {
     Assert.throws(() => new PollPromise(type), /TypeError/);

testing/marionette/transport.js

@@ -10,14 +10,17 @@ const CC = Components.Constructor;
 
 ChromeUtils.import("resource://gre/modules/Services.jsm");
 ChromeUtils.import("resource://gre/modules/EventEmitter.jsm");
-const {StreamUtils} =
-    ChromeUtils.import("chrome://marionette/content/stream-utils.js", {});
-const {Packet, JSONPacket, BulkPacket} =
-    ChromeUtils.import("chrome://marionette/content/packets.js", {});
-
-const executeSoon = function(func) {
-  Services.tm.dispatchToMainThread(func);
-};
+const {
+  StreamUtils,
+} = ChromeUtils.import("chrome://marionette/content/stream-utils.js", {});
+const {
+  BulkPacket,
+  JSONPacket,
+  Packet,
+} = ChromeUtils.import("chrome://marionette/content/packets.js", {});
+const {
+  executeSoon,
+} = ChromeUtils.import("chrome://marionette/content/sync.js", {});
 
 const flags = {wantVerbose: false, wantLogging: false};