revert: "fix: window.open site instance should belong to same browsing instance (#15216)" (#15757)

This reverts commit 8f35198bfb.

spec/chromium-spec.js

@@ -992,11 +992,7 @@ describe('chromium feature', () => {
         contents = null
       })
 
-      // FIXME: Disabled with site isolation ON
-      // Localstorage area is accessed on the browser process
-      // before checking accessibility on the renderer side,
-      // causing illegal origin access renderer termination.
-      xit('cannot access localStorage', (done) => {
+      it('cannot access localStorage', (done) => {
         ipcMain.once('local-storage-response', (event, error) => {
           assert.strictEqual(
             error,