Bug 840360 - Extract reftest-content.js's setTimeout implementation into new Timer.jsm [r=jwalker r=cjones sr=gavin]

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