[Telemetry] Make histograms unimportant by default.

Any results marked important show up on the buildbot's step summary. Histogram
output is too verbose for that. See:
http://build.chromium.org/p/chromium.perf/builders/Linux%20Perf%20%284%29/builds/3113

This brings us back to the previous behavior before page cyclers were converted
to telemetry.

BUG=196411
TEST=tools/perf/run_multipage_benchmarks --browser=system page_cycler tools/perf/page_sets/page_cycler/moz.json

Review URL: https://codereview.chromium.org/12538016

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@188856 0039d316-1c4b-4281-b951-d872f2087c98
3 files changed