Rename ENABLE(DEFAULT_RENDER_THEME) to USE(DEFAULT_RENDER_THEME) to align with the gyp variable name called use_default_render_theme and with the semantics of the USE() macros.

BUG=286578

Review URL: https://codereview.chromium.org/24202004

git-svn-id: svn://svn.chromium.org/blink/trunk@159520 bbb929c8-8fbe-4397-9dbb-9b2b20218538