Add support for converting cc::FilterOperations into an SkImageFilter

This defines a new type of cc::FilterOperation for reference filters, and
defines a method (RenderSurfaceFilters::BuildImageFilter) that builds an
SkImageFilter from a given cc::FilterOperations.

This also removes cc::Layer::SetFilter and cc::LayerImpl::SetFilter.
These were only used when we had a reference filter, but they are no
longer needed now that reference filters can be included in
FilterOperations.

BUG=181613

Review URL: https://codereview.chromium.org/21154002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225329 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225329