Fix analyzer warnings in packages_file_test.dart.

tests/standalone/packages_file_test.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import "dart:async";
 import "dart:io";
-import "dart:isolate";
 import "dart:convert" show JSON;
 import "package:path/path.dart" as p;
-import "package:expect/expect.dart";
 import "package:async_helper/async_helper.dart";
 
 main() async {
   asyncStart();
 
   await test("file: no resolution",
     "%file/main.dart",
     file: {"main": testMain},
     expect: {"foo.x": null});
 
   // An HTTP script with no ".packages" file assumes a "packages" dir.
   await test("http: no resolution", "%http/main.dart",
     http: {"main": testMain},
     expect: {
+      "iroot": "%http/packages/",
       // "foo": null,
       "foo/": "%http/packages/foo/",
       "foo/bar": "%http/packages/foo/bar",
       "foo.x": null,
     });
 
   for (var scheme in ["file", "http"]) {
 
     testScheme(name, main, {expect, files, args, root, config}) {
       return test("$scheme: $name", main, expect: expect,
@@ skipping 204 matching lines @@
                                scriptArgs: args?.map(fixPaths));
     // These expectations are default. If not overridden the value will be
     // expected to be null. That is, you can't avoid testing the actual
     // value of these, you can only change what value to expect.
     // For values not included here (commented out), the result is not tested
     // unless a value (maybe null) is provided.
     var expects = {
        "pconf":   null,
        "proot":   null,
        "iconf":   null,
-       "iconf":   null,
+       "iroot":   null,
        // "foo":   null,
        "foo/":    null,
        "foo/bar": null,
        "foo.x":  "qux",
     }..addAll(expect);
     match(JSON.decode(output), expects, fixPaths, name);
-  } catch (e) {
+  } catch (e, s) {
     // Unexpected error calling runDart or parsing the result.
     // Report it and continue.
     print("ERROR running $name: $e\n$s");
     failingTests.add(name);
   } finally {
     if (https != null) await https.close();
     if (tmpDir != null) tmpDir.deleteSync(recursive: true);
   }
 }
 
@@ skipping 201 matching lines @@
 }
 
 // Counter used to avoid reusing temporary directory names.
 // Some platforms are timer based, and creating two temp-dirs withing a short
 // duration may cause a collision.
 int tmpDirCounter = 0;
 
 Directory createTempDir() {
   return Directory.systemTemp.createTempSync("pftest-${tmpDirCounter++}-");
 }