Expose the BudgetService interface to Workers.

third_party/WebKit/LayoutTests/http/tests/budget/resources/instrumentation-service-worker.js

 // Allows a document to exercise the Budget API within a service worker by sending commands.
 
 self.addEventListener('message', function(workerEvent) {
   port = workerEvent.data;
 
   // Listen to incoming commands on the message port.
   port.onmessage = function(event) {
     if (typeof event.data != 'object' || !event.data.command)
       return;
     var options = event.data.options || {};
@@ skipping 28 matching lines @@
         break;
 
       case 'reserve':
         navigator.budget.reserve('silent-push').then(success => {
           port.postMessage({
             command: event.data.command,
             success: success });
         }).catch(makeErrorHandler(event.data.command));
         break;
 
+      case 'checkInterfaces':
+        var success = false;
+        var message = "";
+        try {
+          if ('BudgetService' in self &&
+              WorkerNavigator.prototype.hasOwnProperty('budget') &&
+              BudgetService.prototype.hasOwnProperty('getCost') &&
+              BudgetService.prototype.hasOwnProperty('getBudget') &&
+              BudgetService.prototype.hasOwnProperty('reserve')
+             )
+            success = true;
+        } catch(err) {
+          message = err.message;
+        }

[Peter Beverloo, 2016/12/12 14:28:43]

What exception do you expect to be thrown here? I don't think there is any.

The following would be much nicer:

const success = 'BudgetService' in self &&
                BudgetService.prototype.hasOwnProperty('getCost') &&
                BudgetService.prototype.hasOwnProperty('getBudget') &&
                BudgetService.prototype.hasOwnProperty('reserve') &&
                WorkerNavigator.prototype.hasOwnProperty('budget');

port.postMessage({ .. });

[harkness, 2016/12/12 16:00:34]

Updated the code to remove the if statement, but left the try in. 

I used that a lot when I was testing because without that, the test just times
out without giving any information if there is an exception. While I was
testing, the exception was because I was using Navigator or navigator instead of
WorkerNavigator, but it could also happen if you accidentally deleted a
character in any of the names, and the timeout is very difficult to debug but
with the exception message, it's quick to track down.

+        port.postMessage({
+          command: event.data.command,
+          success: success,
+          message: message});
+        break;
+
       default:
         port.postMessage({
           command: 'error',
           errorMessage: 'Invalid command: ' + event.data.command });
         break;
     }
   };
 
   // Notify the controller that the worker is now available.
   port.postMessage('ready');
 });
 
 function makeErrorHandler(command) {
   return function(error) {
     var errorMessage = error ? error.message : 'unknown error';
     port.postMessage({
       command: command,
       success: false,
       errorMessage: errorMessage });
   };
 }