[telemetry] Change assertLess to assertTrue.

BUG=None.
TEST=tools/perf/run_tests
R=qyearsley@chromium.org, qyearsley
TBR=nduca

Review URL: https://codereview.chromium.org/27185004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228496 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228496