Remove strict checks on source/target frame roles

These checks had not been updated for the addition of the "profile" application.
Also at a conceptual level the responsibility for deciding which types of frames
are allowed to connect to each other belongs to the `PortProvider` in the host
frame, not the `PortFinder` in other frames.

src/shared/messaging/port-finder.ts

@@ -49,20 +49,6 @@ export class PortFinder implements Destroyable {
    * @param target - the frame aiming to be discovered
    */
   async discover(target: Frame): Promise<MessagePort> {
-    let isValidRequest = false;
-    if (
-      (this._source === 'guest' && target === 'host') ||
-      (this._source === 'guest' && target === 'sidebar') ||
-      (this._source === 'sidebar' && target === 'host') ||
-      (this._source === 'notebook' && target === 'sidebar')
-    ) {
-      isValidRequest = true;
-    }
-
-    if (!isValidRequest) {
-      throw new Error('Invalid request of channel/port');
-    }
-
     const requestId = generateHexString(6);
 
     return new Promise((resolve, reject) => {

src/shared/messaging/test/port-finder-test.js

@@ -87,18 +87,6 @@ describe('PortFinder', () => {
   });
 
   describe('#discover', () => {
-    ['guest', 'invalid'].forEach(target =>
-      it('rejects if requesting an invalid port', async () => {
-        let error;
-        try {
-          await portFinder.discover(target);
-        } catch (e) {
-          error = e;
-        }
-        assert.equal(error.message, 'Invalid request of channel/port');
-      }),
-    );
-
     it('sends port request to host frame', async () => {
       const clock = sinon.useFakeTimers();
       try {
@@ -128,7 +116,7 @@ describe('PortFinder', () => {
       { source: 'sidebar', target: 'host' },
       { source: 'notebook', target: 'sidebar' },
     ].forEach(({ source, target }) =>
-      it('resolves if requesting a valid port', async () => {
+      it('resolves when port is returned', async () => {
         const { port1 } = new MessageChannel();
         let resolvedPort;
         portFinder = createPortFinder(source);