Install from a CRX

[jonathansampson]

Offer users the ability to install a CRX directly.

This request is coming out of a discussion pertaining to a native application that requires a signed version of Brave. Since Brave Software presently only signs release builds, this precludes developers from testing extensions against browser-laptop.

The alternative approach to testing extensions has been to overwrite older extension folders with newer extension bits. For instance, replacing Extension A 3.9 with Extension A 4.0 (while preserving folder structure). When Brave loads, it will attempt to retrieve the older extension bits, and instead receive the newer extension bits. A few factors can complicate the alternative approach, making it ultimately unreliable.

Offering developers the ability to Install from a CRX would side-step both sets of issues.

@bridiver @bbondy, thoughts?

Related issues:

• extension apis would be vulnerable to malicious extensions if we allowed webstore installs #110 extension apis would be vulnerable to malicious extensions if we allowed webstore installs