Pattern scrubbing.

Minor Pattern cleanup in preparation of DisplayList patterns arrival:

* use a repeat mode enum instead of disjoint bools
* rename create() -> createBitmapPattern() (to accomodate
  createDisplatListPattern() later)
* avoid unneeded shader inval when re-applying the same pattern-space
  transform
* remove unused repeat mode & pattern-transform getters

R=schenney@chromium.org, senorblanco@chromium.org

Review URL: https://codereview.chromium.org/445223002

git-svn-id: svn://svn.chromium.org/blink/trunk@179711 bbb929c8-8fbe-4397-9dbb-9b2b20218538