Switch to using SourceLocation universally in service protocol.

runtime/observatory/tests/service/steal_breakpoint_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 --steal-breakpoints
 
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 import 'test_helper.dart';
 import 'dart:async';
 
@@ skipping 34 matching lines @@
 
   await completer.future;  // Wait for breakpoint event to fire.
 },
 
 // We are at the breakpoint on line 14.
 (Isolate isolate) async {
   ServiceMap stack = await isolate.getStack();
   expect(stack.type, equals('Stack'));
   expect(stack['frames'].length, greaterThanOrEqualTo(1));
 
-  Script script = stack['frames'][0]['script'];
+  Script script = stack['frames'][0].location.script;
   await script.load();
   expect(script.name,endsWith('steal_breakpoint_test.dart'));
-  expect(script.tokenToLine(stack['frames'][0]['tokenPos']), equals(14));
+  expect(script.tokenToLine(stack['frames'][0].location.tokenPos), equals(14));
 },
 
 // Resume
 (Isolate isolate) async {
   Completer completer = new Completer();
   var subscription;
   subscription = isolate.vm.events.stream.listen((ServiceEvent event) {
     if (event.kind == ServiceEvent.kResume) {
       print('Isolate resumed');
       subscription.cancel();
       completer.complete();
     }
   });
   isolate.resume();
   await completer.future;
 },
 
 ];
 
 main(args) => runIsolateTests(args, tests, testeeBefore: startTimer);