Set USE(NATIVE_FULLSCREEN_VIDEO) in config.h instead of a gyp file as the gyp build system does not need knowledge about this configuration.

BUG=286578

Review URL: https://chromiumcodereview.appspot.com/23447032

git-svn-id: svn://svn.chromium.org/blink/trunk@158126 bbb929c8-8fbe-4397-9dbb-9b2b20218538