Make several service protocol RPCs private.

runtime/observatory/tests/service/native_metrics_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:profiler';
@@ skipping 11 matching lines @@
     expect(metrics.length, greaterThan(1));
     expect(metrics.length, greaterThan(1));
     var foundOldHeapCapacity = metrics.values.any(
         (m) => m.name == 'heap.old.capacity');
     expect(foundOldHeapCapacity, equals(true));
   },
 
   (Isolate isolate) async {
     var params = { 'metricId': 'metrics/native/heap.old.used' };
     ServiceMetric counter =
-      await isolate.invokeRpc('getIsolateMetric', params);
+      await isolate.invokeRpc('_getIsolateMetric', params);
     expect(counter.type, equals('Counter'));
     expect(counter.name, equals('heap.old.used'));
   },
 
   (Isolate isolate) async {
     bool caughtException;
     try {
-      await isolate.invokeRpc('getIsolateMetric',
+      await isolate.invokeRpc('_getIsolateMetric',
                               { 'metricId': 'metrics/native/doesnotexist' });
       expect(false, isTrue, reason:'Unreachable');
     } on ServerRpcException catch (e) {
       caughtException = true;
       expect(e.code, equals(ServerRpcException.kInvalidParams));
       expect(e.message,
-             "getIsolateMetric: invalid 'metricId' "
+             "_getIsolateMetric: invalid 'metricId' "
              "parameter: metrics/native/doesnotexist");
     }
     expect(caughtException, isTrue);
   },
 
 ];
 
 main(args) => runIsolateTests(args, tests, testeeBefore: script);