Fix squashing to treat perspective and preserve3d elements as transform ancestors.

This is necessary because they can affect the local transform of an element, so
elements with different perspecitive/transform3d ancestors cannot squash together.

BUG=404953,403819
R=vollick@chromium.org

Review URL: https://codereview.chromium.org/497153003

git-svn-id: svn://svn.chromium.org/blink/trunk@180799 bbb929c8-8fbe-4397-9dbb-9b2b20218538