Revert "5/N Remove PluginInitializer entirely."

Revert submission 15560568-b194781951-flags-8

Reason for revert: Broken build.
Reverted Changes:
Ie522ae3cc:5/N Remove PluginInitializer entirely.
Icaeaaee28:4/N Remove #handleWtfs from PluginInitializer.
I1c86c246c:3/N Remove #getPrivilegedPlugins from PluginInitia...
Id525f27e3:2/N Rename PluginInstanceManager to PluginActionMa...

Change-Id: I417dd4eddb0216e351a4eb1870a35f3ebc84045a