[Merge] lp:~abreu-alexandre/webbrowser-app/remove-session-storage into lp:webbrowser-app

[Olivier Tilloy]

Tested again on flo #243 (utopic-proposed) with silo 3, I can reliably reproduce the crash when running the webapp_container autopilot tests. Crash file uploaded there: http://people.canonical.com/~osomon/_usr_bin_webapp-container.32011.crash
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https://code.launchpad.net/~abreu-alexandre/webbrowser-app/remove-session-storage/+merge/234144
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