Make methods in Stopwatch getters and rename to be more consistent.

tests/benchmark_smoke/benchmark_base.dart

Index: tests/benchmark_smoke/benchmark_base.dart
diff --git a/tests/benchmark_smoke/benchmark_base.dart b/tests/benchmark_smoke/benchmark_base.dart
index 5aac45011f7dfa9a1f21756f3e06c8c296218d25..41a3729ad958cca62467920a1b1ba093fcbbbcf7 100644
--- a/tests/benchmark_smoke/benchmark_base.dart
+++ b/tests/benchmark_smoke/benchmark_base.dart
@@ -60,7 +60,7 @@ class BenchmarkBase {
     int elapsed = 0;
     while (elapsed < timeMinimum || iter < 32) {
       f();
-      elapsed = watch.elapsedInMs();
+      elapsed = watch.elapsedMilliseconds;
       iter++;
     }
     return (1000.0 * iter) / elapsed;