Move SerializedScriptValue wire format version to public header

R=jamesr@chromium.org,haraken@chromium.org
BUG=299125

Review URL: https://chromiumcodereview.appspot.com/24876004

git-svn-id: svn://svn.chromium.org/blink/trunk@158478 bbb929c8-8fbe-4397-9dbb-9b2b20218538