Improve presentation of aggregate results in mojo_benchmark.

This prints median, mean and std-dev of each measurement when running
with `--aggregate`.

R=qsr@chromium.org

Review URL: https://codereview.chromium.org/1442623002 .

Cr-Mirrored-From: https://github.com/domokit/mojo
Cr-Mirrored-Commit: 70faf5f60271f65f8984646751bccdf74ddcedf6

mojo_benchmark

diff --git a/mojo_benchmark b/mojo_benchmark
index 9a4803c..e01ff62 100755
--- a/mojo_benchmark
+++ b/mojo_benchmark
@@ -7,6 +7,7 @@
 
 import argparse
 import logging
+import numpy
 import sys
 import time
 
@@ -70,6 +71,16 @@
   print '-' * 72
 
 
+def _format_vector(results):
+  if not len(results):
+    return "med -, avg -, std-dev -, (no results)"
+
+  return "med %f, avg %f, std-dev %f %s" % (numpy.median(results),
+                                                numpy.mean(results),
+                                                numpy.std(results),
+                                                str(results))
+
+
 def _print_results(benchmark_name, variant_name, results, measurements,
                    aggregate):
   print '[ %s ] %s ' % (benchmark_name, variant_name)
@@ -77,7 +88,7 @@
     print '  ' + measurement['name'] + ': ',
     if measurement['spec'] in results:
       if aggregate:
-        print str(results[measurement['spec']])
+        print _format_vector(results[measurement['spec']])
       else:
         if len(results[measurement['spec']]) == 0:
           print '?'