[telemetry] Adjust my prior fix to not wait for the tab to complete loading when we did not just launch the browser.  In the case where we did not just launch the browser, the previously loaded page may never complete loading so we may wait indefinitely.

R=dtu@chromium.org, tonyg
BUG=307798

Review URL: https://codereview.chromium.org/27183014

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228977 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228977