Need a mechanism to handle per-platform differences.

[jeffdav]

Specifically, we define custom error codes for WinAppDriver, but those same codes could mean different things on platforms targeting different engines. We should handle platform specific errors in some sort of "what platform am I on?" block.

[tristanlabelle]

@jeffdav Could we say that #115 completes this (if we merge it)?

[jeffdav]

Not quite, because, as you noted in your diff, there's a WAD-specfiic error code. We need some way of delegating the "what errors should trigger a retry" out to platform specific modules.

[jeffdav]

But #115 is a great start!