[telemetry] Preserve trailing slashes in URLs.

Some page cyclers use relative URLs in the HTML page, so navigating to the URL without the slash was giving 404s for those resources. That would artificially lower the page cycler times.

BUG=None.
TEST=tools/telemetry/run_tests testPage; tools/perf/run_benchmark page_cycler.bloat # Look for trailing slash in omnibox.
R=tonyg@chromium.org

Review URL: https://codereview.chromium.org/27963002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229446 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 229446