Stop caching the result of shouldLoadTabInBackground(), there's no point since we need to look at the state of the shift key every time, and we didn't update it in all code paths to begin with.
Pass in |event| from more places in history and bookmarks so we'll actually look at te shift key.
Replace use of "tab_background" with looking at shouldLoadTabInBackground().
r=IanN, sr=Neil
git-svn-id: svn://10.0.0.236/trunk@205199 18797224-902f-48f8-a5cc-f745e15eee43
5e048c7dd0