[SysApps] Compile Chromium's StorageMonitor as a module

The StorageMonitor is almost self-contained, despite adding itself
to the Chromium's Browser Process. We should work upstream to fix that.

Meanwhile we can compile it as module (and protect the Chromium specific bits
with a flag) so we can use it as backend for the Device Capabilities
getStorageInfo() for Linux, Mac and Windows.
[SysApps] Add a data provider for Linux based on Chromium's StorageMonitor

This provider has a big chance of being generic enough to be used for Mac and
Windows. The backend for Android was not implemented yet which makes me sad.

We will have to implement a custom provider for Android (upstream maybe?).
[SysApps] Add a simple test for Device Capabilities

Not to self: make a browsertest out of this. :)