cc: Minor clean ups to ETC1PixelRef header.

- remove unnecessary includes
- use chromium OVERRIDE macro instead of skia SK_OVERRIDE.
- use DISALLOW_COPY_AND_ASSIGN macro.

BUG=None
TEST=cc_unittests
R=enne@chromium.org,jamesr@chromium.org

Review URL: https://codereview.chromium.org/67613002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234110 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 234110