Add ability to run dartium in arbitrary profile

[Rodsevich]

When running dartium it creates it's own ad hoc profile in the /tmp dir, which takes long enough time to fill before the browser justs opens.
If, I think everybody, downloads dartium just to tests theirs own Dart projects, why would those profiles be created instead of a single one that would be used several times?

[zoechi]

That would hurt reproducibility. What if your profile has some history data (localstorage or whatever), plugins, ..., that influence tests, then you might wonder eventually why the test run a while ago but doesn't anymore? Starting with a clean slate avoids that.

[Rodsevich]

And what about preloading that custom profile made in /tmp with the minimal profile customized by user:

1. I configure my own desired profile
2. I make a copy of that profile in, i.e. /etc/dartium/dart_tests/default_profile
3. test executes and, in addition to creating the ad hoc /tmp profile, it populates it with the contents of the previous point

[zoechi]

That definitely makes more sense to me.

[nex3]

This is something we could probably support in the config file once we have configurable platforms (#391).

[patkujawa-wf]

How about now? :)

[matanlurey]

Dartium has been discontinued so I don't think this is planned.