Auto merge of #12910 - creativcoder:swsender, r=jdm

Implement postMessage for ServiceWorkers

<!-- Please describe your changes on the following line: -->

Fixes #12773
r? @jdm

Changes:
* Implements `postMessage` on `ServiceWorker` object.
* Removes unused channels from sw and their scopes.
* Fixes a crash when calling `scope.script_chan()` in sw-scopes event handling.

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #12773

<!-- Either: -->
- [X] There are tests for these changes at `tests/html/service-worker`

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

<!-- Reviewable:start -->
---
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tests/html/service-worker/demo_iframe.html

@@ -8,6 +8,5 @@
 <div>
 <a href="http://github.com/servo/servo">Servo Project</a>
 </div>
-
 </body>
 </html>

tests/html/service-worker/dummy.js

@@ -0,0 +1,3 @@
+function test_importScripts() {
+	console.log('Hi from dummy.js');
+}

tests/html/service-worker/iframe_sw.js

@@ -1,7 +1,11 @@
 self.addEventListener('activate', function(e) {
-	console.log("iframe service worker active");
+    console.log("iframe service worker active");
 });
 
 self.addEventListener('fetch', function(e) {
-	console.log("A fetch event detected by /iframe service worker");
-});
+    console.log("A fetch event detected by /iframe service worker");
+});
+
+self.addEventListener('message', function(e) {
+    console.log(e.data.payload.msg + ' from '+ e.data.payload.worker_id);
+})

tests/html/service-worker/index.html

@@ -16,36 +16,56 @@
     <button onclick="register_zero()">Register for Root (/)</button>
     <button onclick="register_one()">Register for Dashboard (/dashboard)</button>
     <button onclick="register_two()">Register for Profile (/profile)</button>
+    <button onclick="post_message_root()">Msg to Root service worker</button>
 </div>
-
     <script>
+
     var reg = navigator.serviceWorker.register('iframe_sw.js', { 'scope': '/demo_iframe.html' });
     console.log("From client worker registered: ", navigator.serviceWorker.controller);
     console.log("Registered script source: "+ navigator.serviceWorker.controller.scriptURL);
     document.getElementById('iframe_sw').src = 'demo_iframe.html';
+    post_message('/demo_iframe');
 
     function register_zero() {
-        var reg = navigator.serviceWorker.register('sw.js', { 'scope': './' });
+        var reg = navigator.serviceWorker.register('sw.js', { 'scope': './*' });
         console.log("From client worker registered: ", navigator.serviceWorker.controller);
         console.log("Registered script source: "+ navigator.serviceWorker.controller.scriptURL);
     }
 
+    function post_message_root() {
+        // Testing repeated calls of postMessage
+        for(var i=0;i<100;i++){
+            navigator.serviceWorker.controller.postMessage({num:'Dummy message count: '+i});
+        }
+    }
+
     function register_one() {
         var reg = navigator.serviceWorker.register('sw_dashboard.js', { 'scope': '/dashboard' });
         console.log("From client worker registered: ", navigator.serviceWorker.controller);
         console.log("Registered script source: "+ navigator.serviceWorker.controller.scriptURL);
+        post_message('/dashboard');
     }
 
     function register_two() {
         var reg = navigator.serviceWorker.register('sw_profile.js', { 'scope': '/profile' });
         console.log("From client worker registered: ", navigator.serviceWorker.controller);
         console.log("Registered script source: "+ navigator.serviceWorker.controller.scriptURL);
+        post_message('/profile');
     }
 
     navigator.serviceWorker.addEventListener('controllerchange', function(e) {
-        console.log("active Service Worker changed");
+        console.log("navigator.serviceWorker.controller changed");
     });
 
+    function post_message(worker_id) {
+        navigator.serviceWorker.controller.postMessage({
+        payload:{
+            msg:'Hi there! This is a dummy message for testing of postMessage calls from Service Workers',
+            worker_id:worker_id
+            }
+        });
+    }
+
     </script>
 </body>
 </html>

tests/html/service-worker/sw.js

@@ -0,0 +1,11 @@
+self.addEventListener('activate', function(e) {
+    console.log('Root service worker active');
+});
+
+self.addEventListener('fetch', function(e) {
+    console.log("A fetch event detected by / service worker");
+});
+
+self.addEventListener('message', function(e) {
+    console.log(e.data.num);
+})

tests/html/service-worker/sw_dashboard.js

@@ -1,9 +1,11 @@
-importScripts('dashboard_helper.js');
-
 self.addEventListener('activate', function(e) {
-	status_from_dashboard();
+    console.log('Dashboard service worker active');
 });
 
 self.addEventListener('fetch', function(e) {
-	console.log("A fetch event detected by /dashboard service worker");
-});
+    console.log("A fetch event detected by /dashboard service worker");
+});
+
+self.addEventListener('message', function(e) {
+    console.log(e.data.payload.msg + ' from '+ e.data.payload.worker_id);
+})

tests/html/service-worker/sw_profile.js

@@ -1,8 +1,12 @@
 
 self.addEventListener('activate', function(e) {
-	console.log("profile service worker active");
+    console.log("profile service worker active");
 });
 
 self.addEventListener('fetch', function(e) {
-	console.log("A fetch event detected by /profile service worker");
-});
+    console.log("A fetch event detected by /profile service worker");
+});
+
+self.addEventListener('message', function(e) {
+    console.log(e.data.payload.msg + ' from '+ e.data.payload.worker_id);
+})