Redo our benchmarks; add a benchmark/benchmarks.dart tool.

pkg/analysis_server/benchmark/readme.md

+# Analysis Server Benchmarks
+
+## How to run the benchmarks
+
+To see a list of all available benchmarks, run:
+
+```
+dart benchmarks/benchmarks.dart list
+```
+
+To run an individual benchmark, run:
+
+```
+dart benchmarks/benchmarks.dart run <benchmark-id>
+```
+
+## How they're tested
+
+In order to make sure that our benchmarks don't regress in terms of their
+ability to run, we create one unit test per benchmark, and run those tests
+as part of our normal CI test suite.
+
+To save time on the CI, we only run one iteration of each benchmark
+(`--repeat=1`), and we run the benchmark on a smaller data set (`--quick`).
+
+See `test/benchmark_test.dart`.
+
+## To add a new benchmark
+
+Register the new benchmark in then main() method of benchmarks/benchmarks.dart.
+
+## On the bots
+
+Our benchmarks run on a continuous performance testing system. It will run
+any benchmark produced by the `benchmarks/benchmarks.dart list` command.
+
+To not run a benchmark on the bot, define the benchmark with the `disable` flag.