Pass Compositor to EffectsHandlerImpl

Obsoletes the need to go through the Workspace object to get to
the Compositor.

TODO for future: make the Compositor being the parent object for
the EffectsHandlerImpl.

Closing Review and bug from this commit, which is the top most
of the patch series.

REVIEW: 106060
BUG: 299277
FIXED-IN: 4.10