RELAND: [Telemetry] Shortcut browser finding when an explicit --browser is given.

Browser finding on cros and android takes a little bit of time. If we are
given a --browser, there's no need to do it.

BUG=
TBR=bulach@chromium.org

Review URL: https://codereview.chromium.org/68173010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234825 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 234825