Delete CompositingProperties.

This tries to separate out the properties that are updating
during compositing, but in the process leads to worse bit packing
and is just confusing because the code doesn't do anything.
We could add comments before each of these properties and
have the same benefit.

Eventually, we should probably assert that compositing is
up to date in the getters for these properties.

Review URL: https://codereview.chromium.org/242493004

git-svn-id: svn://svn.chromium.org/blink/trunk@171992 bbb929c8-8fbe-4397-9dbb-9b2b20218538