Allow benchmarks to provide the standard deviation.

Allow benchmarks to provide the standard deviation.

Some benchmarks include their own runner which provides an
overall average and a standard deviation. This enables
extraction of that value similar to the other measurements.

These benchmarks should only be run once. If a benchmarks
specifies multiple runs and provides a standard deviation,
a warning will be issued that makes the build fail on the
buildbot side.

TEST=python -m unittest run_benchmarks_test
BUG=393947
LOG=n
R=jkummerow@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=22424

[Michael Achenbach, 2014-07-16 08:30:23]

PTAL

[Jakob Kummerow, 2014-07-16 08:38:29]

LGTM except for naming.

"stderr" is the standard output stream for error messages (stdout's evil twin).
Please use "standard_deviation" or "deviation" (or "stddev", if you absolutely
have to abbreviate) both in the CL description and all over the code.

[Michael Achenbach, 2014-07-16 08:49:04]

On 2014/07/16 08:38:29, Jakob wrote:
> LGTM except for naming.
> 
> "stderr" is the standard output stream for error messages (stdout's evil
twin).
> Please use "standard_deviation" or "deviation" (or "stddev", if you absolutely
> have to abbreviate) both in the CL description and all over the code.

Done.

[Michael Achenbach, 2014-07-16 08:53:57]

Committed patchset #2 manually as r22424 (presubmit successful).