[js] Fire the "uncaughtException" event in a new turn of the JS event loop.

As a result of this change, any errors thrown by an event listener will
propagate to the global error handler. Previously, this event was fired with in
the context of a (native) promise callback, causing errors to be silently
suppressed in the promise chain.

This was tested manually. I'm not sure how to test interaction with node's
global error handler using mocha (without crashing the process)

Fixes #2770

Author: jleyba

javascript/node/selenium-webdriver/CHANGES.md

@@ -8,6 +8,11 @@
   via tha API, `safari.Options#useLegacyDriver`, to use the safari
   extension driver.
 * Updated the `lib/proxy` module to support configuring a SOCKS proxy.
+* For the `promise.ControlFlow`, fire the "uncaughtException" event in a new
+  turn of the JS event loop. As a result of this change, any errors thrown by
+  an event listener will propagate to the global error handler. Previously,
+  this event was fired with in the context of a (native) promise callback,
+  causing errors to be silently suppressed in the promise chain.
 
 ### API Changes
 

javascript/node/selenium-webdriver/lib/promise.js

@@ -644,18 +644,6 @@ function asyncRun(fn) {
 }
 
 
-/**
- * Throws an error asynchronously so it is reported to the global error handler.
- *
- * @param {!Error} error The error to throw.
- */
-function asyncThrow(error) {
-  setTimeout(function() {
-    throw error;
-  }, 0);
-}
-
-
 /**
  * @param {number} level What level of verbosity to log with.
  * @param {(string|function(this: T): string)} loggable The message to log.
@@ -2297,13 +2285,14 @@ class ControlFlow extends events.EventEmitter {
     this.cancelShutdown_();
     this.cancelHold_();
 
-    var listeners = this.listeners(
-        ControlFlow.EventType.UNCAUGHT_EXCEPTION);
-    if (!listeners.size) {
-      asyncThrow(/** @type {!Error} */(error));
-    } else {
-      this.reportUncaughtException_(error);
-    }
+    setTimeout(() => {
+      let listeners = this.listeners(ControlFlow.EventType.UNCAUGHT_EXCEPTION);
+      if (!listeners.size) {
+        throw error;
+      } else {
+        this.reportUncaughtException_(error);
+      }
+    }, 0);
   }
 
   /**

javascript/node/selenium-webdriver/test/lib/promise_test.js

@@ -96,7 +96,10 @@ describe('promise', function() {
       // so tearDown() doesn't throw
       app.removeAllListeners();
       app.on(promise.ControlFlow.EventType.UNCAUGHT_EXCEPTION, handler);
-      return NativePromise.resolve().then(() => handler.assertCalled());
+      return NativePromise.resolve()
+          // Macro yield so the uncaught exception has a chance to trigger.
+          .then(() => new NativePromise(resolve => setTimeout(resolve, 0)))
+          .then(() => handler.assertCalled());
     });
   });
 
@@ -312,7 +315,10 @@ describe('promise', function() {
     app.removeAllListeners();
     app.on(promise.ControlFlow.EventType.UNCAUGHT_EXCEPTION, handler);
 
-    return NativePromise.resolve().then(handler.assertCalled);
+    return NativePromise.resolve()
+        // Macro yield so the uncaught exception has a chance to trigger.
+        .then(() => new NativePromise(resolve => setTimeout(resolve, 0)))
+        .then(handler.assertCalled);
   });
 
   it('cannotResolveADeferredWithItself', function() {