This allows plugins to depend on bower_component libraries (deps of
polygerrit_plugin and polygerrit_bundle are always bower components,
see also the 'zips' variable in _bundle_impl).
This prepares a fix in the image-diff plugin, which had to use an asset
to pull in the resemblejs library, which made it more complicated and
more difficult to import into google3.
Change-Id: Idb562f44f5781b6e588a156a44cd39f853afaec6
027551fb11