Bug 1050447 - Skip focusing content if we're opening a new about:blank or about:newtab tab. r=dao, feedback=jimm.

This fixes a change in order of focus events for e10s after bug 1009628 landed.
We were accidentally focusing the content after focusing the URL bar for new
tabs. We now skip focusing the content entirely when opening a new tab.

--HG--
extra : histedit_source : a6c140d4e2b4677209b039880922c29e7c24b584