Filter out shorthands for make_computed_style_base.py.

This patch filters out shorthands from the input of
make_computed_style_base. This is to explictly prevent shorthands being
treated like CSS properties in ComputedStyle.

Currently there are no shorthands being generated as properties, so this
patch does not affect behaviour.

BUG=628043

Review-Url: https://codereview.chromium.org/2809053002
Cr-Commit-Position: refs/heads/master@{#464307}
1 file changed