Bug 871081: Share a common RootActor implementation amongst browser, Fennec, B2G, and xpcshell tests. r=past,mfinkle,fabrice

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rename : browser/devtools/debugger/test/browser_dbg_listtabs.js => browser/devtools/debugger/test/browser_dbg_listtabs-01.js
Bug 866950 - Errors from files loaded through loader.js not showing source in browser console; r=robcee
Bug 877778 - Browser Console, clicking JS/CSS error/warning link does not open source file; r=robcee