Bug 1287229 - port.disconnect should not throw r=billm

MozReview-Commit-ID: 7d8Zmb4OAd0

--HG--
extra : rebase_source : 6766832c0081679eadf1bdbc1576f8b554c68e3c

toolkit/components/extensions/ExtensionUtils.jsm

@@ -1048,7 +1048,9 @@ Port.prototype = {
 
   disconnect() {
     if (this.disconnected) {
-      throw new this.context.contentWindow.Error("Attempt to disconnect() a disconnected port");
+      // disconnect() may be called without side effects even after the port is
+      // closed - https://developer.chrome.com/extensions/runtime#type-Port
+      return;
     }
     this.handleDisconnection();
     this.messageManager.sendAsyncMessage(this.disconnectName);

toolkit/components/extensions/test/mochitest/test_ext_runtime_disconnect.html

@@ -17,6 +17,9 @@ function backgroundScript() {
   browser.runtime.onConnect.addListener(port => {
     browser.test.assertEq(port.name, "ernie", "port name correct");
     port.onDisconnect.addListener(() => {
+      // Closing an already-disconnected port is a no-op.
+      port.disconnect();
+      port.disconnect();
       browser.test.sendMessage("disconnected");
     });
     browser.test.sendMessage("connected");