I needed to run telemetry_perf_unittests to diagnose a flake (https://build.chromium.org/p/tryserver.chromium.android/builders/android_n5x_swarming_rel/builds/116501), but it took 20 minutes of two engineer's time to figure out how to do so.  The error when you try to run that target is not very useful:

$ cr run telemetry_perf_unittests 
ninja: Entering directory `/usr/local/google/code/clankium/src/out_android/Release'
ninja: no work to do.
C    0.005s Main  Could not find apk or executable for telemetry_perf_unittests
E    0.006s Main  Unrecognized error occurred.
Traceback (most recent call last):
  File "/usr/local/google/code/clankium/src/build/android/test_runner.py", line 834, in main
    return RunTestsCommand(args)
  File "/usr/local/google/code/clankium/src/build/android/test_runner.py", line 629, in RunTestsCommand
    return RunTestsInPlatformMode(args)
  File "/usr/local/google/code/clankium/src/build/android/test_runner.py", line 715, in RunTestsInPlatformMode
    test_instance = test_instance_factory.CreateTestInstance(args, infra_error)
  File "/usr/local/google/code/clankium/src/build/android/pylib/base/test_instance_factory.py", line 18, in CreateTestInstance
    args, device_dependencies.GetDataDependencies, error_func)
  File "/usr/local/google/code/clankium/src/build/android/pylib/gtest/gtest_test_instance.py", line 306, in __init__
    error_func('Could not find apk or executable for %s' % self._suite)
  File "/usr/local/google/code/clankium/src/build/android/test_runner.py", line 661, in infra_error
    sys.exit(constants.INFRA_EXIT_CODE)
SystemExit: 87

After some hunting it turned out we need to specify a --browser parameter, but that doesn't actually work:

$ cr run telemetry_perf_unittests --browser=android-chromium
ninja: Entering directory `/usr/local/google/code/clankium/src/out_android/Release'
ninja: no work to do.
usage: test_runner.py [-h]
                      {gtest,instrumentation,junit,linker,monkey,perf,python}
                      ...
test_runner.py: error: unrecognized arguments: --browser=android-chromium
Error 2 executing command ['/usr/local/google/code/clankium/src/build/android/test_runner.py', 'gtest', '-s', 'telemetry_perf_unittests', '--release', '--browser=android-chromium']

More spelunking later and we figured out this command was needed:

tools/perf/run_tests -v --browser=android-chromium

Can we please add a print somewhere obvious in the bot stdout so the next person who needs to do this doesn't have a bad time?  Thanks!