Fix plumbing of transformOrigin in cases where there is a
default value for -webkit-transform-origin.

Also, add debug output for transformOrigin in layer dumps,
and initialize transformOrigin in a few places.

Review URL: https://codereview.chromium.org/294163014

git-svn-id: svn://svn.chromium.org/blink/trunk@175330 bbb929c8-8fbe-4397-9dbb-9b2b20218538