Implement WebPushProvider.unregister() in Chromium.

chrome/test/data/push_messaging/test.html

Index: chrome/test/data/push_messaging/test.html
diff --git a/chrome/test/data/push_messaging/test.html b/chrome/test/data/push_messaging/test.html
index 66b6e2f615bb890c652e8d8dd4b5ee464712d726..e48d371921428c52e4005aa230b54e20886ebf0e 100644
--- a/chrome/test/data/push_messaging/test.html
+++ b/chrome/test/data/push_messaging/test.html
@@ -5,6 +5,7 @@
   <link rel="manifest" href="manifest.json">
   <script>
     var pushData = new FutureData();
+    var pushRegistration = null;
 
     // Sends data back to the test. This must be in response to an earlier
     // request, but it's ok to respond asynchronously. The request blocks until
@@ -88,7 +89,8 @@
       navigator.serviceWorker.ready.then(function(swRegistration) {
         // TODO(mvanouwerkerk): Cleanup once the final API is exposed.
         var pushManager = swRegistration.pushManager || navigator.push;
-        pushManager.register().then(function(pushRegistration) {
+        pushManager.register().then(function(registration) {
+          pushRegistration = registration;
           sendResultToTest(pushRegistration.pushEndpoint + ' - ' +
               pushRegistration.pushRegistrationId);
         }, sendErrorToTest);
@@ -113,6 +115,17 @@
       }
     }
 
+    function unregister() {
+      if (!pushRegistration) {
+        sendErrorToTest('no registration');
+        return;
+      }
+
+      pushRegistration.unregister().then(function(result) {
+        sendResultToTest('unregister result: ' + result);
+      });
+    }
+
     addEventListener('message', function(event) {
       var message = JSON.parse(event.data);
       if (message.type == 'push') {