Moved class definitions into header

Change-Id: I2d3e5ec6f8f5068284cdbaa6900797950fc7e01a
Reviewed-on: https://chromium-review.googlesource.com/c/1422739
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58946}