Support setting mount points in fake image loader client

Adds logic to register and load/unload components to fake image loader
client, so it can be used to test code that depends on image loader
client.

Introduces SetMountPathForComponent that sets up mount points
LoadComponent/LoadComponentAtPath return as component's mount point when
called (if a mount point has not been set, the LoadComponent methods
will fail).

Implements logic to register/remove components - it keeps mapping from a
registered component name to its version in memory.

BUG=863162

Change-Id: Iffa3504fc92d495cc46a35caffd3acdd4b7038c8
Reviewed-on: https://chromium-review.googlesource.com/1145463
Commit-Queue: Toni Barzic <tbarzic@chromium.org>
Reviewed-by: Dan Erat <derat@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576956}
2 files changed