Bug 992560 - Make console.time available to content scripts

I have tested this in up-to-date nightly firefox on windows xpp.

It works fine when I build the xpi with

```
AichnerAd@Kuckuck:~/tmp/mozilla/SnapperFirefox/Snapper$ cmd /c "%HOME%/tmp/mozilla/addon-sdk/bin/activate && cfx xpi --force-mobile --no-strip-xpi --force-use-bundled-sdk -b c:/programme/nightly/firefox.exe -v" # Use --no-strip-xpi to ship  Addon-SDK in XPI file
Welcome to the Add-on SDK. For the docs, visit https://addons.mozilla.org/en-US/developers/docs/sdk/latest/
Exporting extension to snapper.xpi.
AichnerAd@Kuckuck:~/tmp/mozilla/SnapperFirefox/Snapper$
```
The browser console logs this when the content script is loaded:

```14:14:25.493 loading started at jar:file:///C:/Dokumente%20und%20Einstellungen/AichnerAd/Anwendungsdaten/Mozilla/Firefox/Profiles/xwlwa1jh.default-1385301407992/extensions/jid1-HE38Y6vsW9TpHg@jetpack.xpi!/bootstrap.js
() takes: timer started sandbox.js:297
14:14:25.495 loading started at jar:file:///C:/Dokumente%20und%20Einstellungen/AichnerAd/Anwendungsdaten/Mozilla/Firefox/Profiles/xwlwa1jh.default-1385301407992/extensions/jid1-HE38Y6vsW9TpHg@jetpack.xpi!/bootstrap.js
() takes: 2ms sandbox.js:297```

I would prefer to sort the keys in the `Object.freeze` argument lexically for readability.

Let me know if I should add that in another commit.

Hope this is deemed useful,
Adrian