Set geometry dirty bits on composited layer mappings when updating squashed layers.

The lack of setting geometry dirty bits in these cases is wrong. However, at the moment it is masked by setting needs geometry dirty bits more globally upwards in the system. When that is cleaned up these targeted ones will be in place.

BUG=

Review URL: https://codereview.chromium.org/200623006

git-svn-id: svn://svn.chromium.org/blink/trunk@169395 bbb929c8-8fbe-4397-9dbb-9b2b20218538