chore(benchmarks): enable transformer on the benchmarks

Closes angular#3960

Author: harryterkelsen

modules/benchmarks/pubspec.yaml

@@ -24,7 +24,7 @@ transformers:
  - web/src/largetable/largetable_benchmark.dart
  - web/src/naive_infinite_scroll/index.dart
  - web/src/tree/tree_benchmark.dart
- generate_change_detectors: false
+ generate_change_detectors: true
 - $dart2js:
  minify: false
  commandLineOptions: