chromium: Update all channels to latest versions

Overview of updated versions:

stable: 54.0.2840.71 -> 54.0.2840.90
beta:   55.0.2883.21 -> 55.0.2883.35
dev:    56.0.2897.0  -> 56.0.2906.0

This is to get our Chromium versions in par with the latest upstream
ones before merging in the GN migration changes.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>