Upstream service wrkr `importScripts` tests to WPT

third_party/WebKit/LayoutTests/http/tests/serviceworker/resources/import-scripts-worker.js

-importScripts('../../resources/testharness.js');
-
-let echo_output = null;
-
-// Tests importing a script that sets |echo_output| to the query string.
-function test_import(str) {
-  importScripts('echo.php?' + str);
-  assert_equals(echo_output, str);
-}
-
-test_import('root');
-test_import('root-and-message');
-
-self.addEventListener('install', () => {
-    test_import('install');
-    test_import('install-and-message');
-  });
-
-self.addEventListener('message', e => {
-    test_import('root-and-message');
-    test_import('install-and-message');
-    // TODO(falken): This should fail. The spec disallows importing a non-cached
-    // script like this but currently Chrome and Firefox allow it.
-    test_import('message');
-    e.source.postMessage('OK');
-  });