Make observatory tests analyzer clean

runtime/observatory/tests/service/pause_on_exceptions_test.dart

 // Copyright (c) 2015, 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.
 // VMOptions=--compile_all --error_on_bad_type --error_on_bad_override
 
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 import 'test_helper.dart';
 import 'dart:async';
-import 'dart:developer';
 
 doThrow() {
   throw "TheException"; // Line 13.
   return "end of doThrow";
 }
 
 doCaught() {
   try {
     doThrow();
   } catch (e) {}
@@ skipping 82 matching lines @@
 
   await test("none", "doCaught()", false, true);
   await test("none", "doUncaught()", false, false);
 
   subscription.cancel();
 },
 
 ];
 
 main(args) => runIsolateTests(args, tests);