Add tests for updating transform and opacity of a squashed layer owner.

These tests exercise CompositedLayerMapping::updateTransform and CompositedLayerMapping::updateOpacity in the case of a squashing layer.

BUG=

Review URL: https://codereview.chromium.org/186963003

git-svn-id: svn://svn.chromium.org/blink/trunk@169167 bbb929c8-8fbe-4397-9dbb-9b2b20218538