Jarvis crashed when experimental features are selected in _deployed_ version

[chseifert]

The bug does only appear when the extension is loaded from webstore, not in the version installed from source code (although both use the same code).

Tested:
Chrome Version 44.0.2403.157 (64-bit)
Jarvis commit dddaa82, deployed version 0.61

To Reproduce:
EITHER

1. Install from webstore (JARVIS), not "dev"
2. Enable experimental features
3. Hit Search
   --> Jarvis icon vanishes, chrome://extensions/ reports "Jarvis 0.61 This extension may have been corrupted."

OR

1. Install from webstore (JARVIS), not "dev"
2. Hit Search (normal search result lists are accessible)
3. Enable experimental features -> "results by provider" button appear
4. Click "results by provider" button
   --> Jarvis icon vanishes, chrome://extensions/ reports "Jarvis 0.61 This extension may have been corrupted."