Bug 842609: Scroll to selected tab in tabs ui. [r=mfinkle]

--HG--
rename : toolkit/modules/Timer.jsm => browser/devtools/shared/Browser.jsm
rename : toolkit/modules/tests/xpcshell/test_timer.js => browser/devtools/shared/test/browser_browser_basic.js
extra : rebase_source : c5a6cb3d09bd673b4ac01afa90de9bc8f350601b