Fix recently introduced strong-mode errors

pkg/analysis_server/benchmark/perf/analysis_timing_tests.dart

Index: pkg/analysis_server/benchmark/perf/analysis_timing_tests.dart
diff --git a/pkg/analysis_server/benchmark/perf/analysis_timing_tests.dart b/pkg/analysis_server/benchmark/perf/analysis_timing_tests.dart
index 3e3af149490f18db2d7157fd4dd079002ea3d151..60aaa7201b996a20691e8a29b9fa131cb81c0deb 100644
--- a/pkg/analysis_server/benchmark/perf/analysis_timing_tests.dart
+++ b/pkg/analysis_server/benchmark/perf/analysis_timing_tests.dart
@@ -44,7 +44,7 @@ main(List<String> arguments) {
     test = new SubscriptionTimingTest();
   }
 
-  Future.wait([test.test_timing()]);
+  Future.wait(<Future>[test.test_timing()]);

[Jennifer Messerly, 2016/09/15 21:00:33]

maybe put a type on "var test" above? Then it wouldn't be needed here

[Brian Wilkerson, 2016/09/15 21:37:26]

The superclass of those two classes doesn't define `test_timing`, so we get a
different error.

 }
 
 const DEFAULT_METRIC = 'analysis';
@@ -103,8 +103,8 @@ class Metric {
 class SubscriptionTimingTest extends AbstractTimingTest {
   List<Metric> _metrics;
 
-  List<Metric> get metrics =>
-      _metrics ??= metricNames.map((name) => getMetric(name)).toList();
+  List<Metric> get metrics => _metrics ??=
+      new List<Metric>.from(metricNames.map((name) => getMetric(name)));

[Jennifer Messerly, 2016/09/15 21:00:33]

any idea what happened here? it doesn't look like something that would be
affected by any recent changes.

also just noticed, it could be: metricNames.map(getMetric)

[Brian Wilkerson, 2016/09/15 21:37:26]

Nope. I tried to reproduce the error and couldn't, so I reverted the change...
...except for this simplification.

 
   Metric getMetric(String name) {
     switch (name) {