Use UNLIKELY() macro in generated bindings for minimum argument count checks

Use UNLIKELY() macro in generated bindings for minimum argument count checks
in as a speculative fix for a performance regression caused by making
arguments mandatory. It is very unlikely the functions are called without the
required number of arguments so we should minimize the impact of this check
on performance.

R=haraken
BUG=285069

Review URL: https://chromiumcodereview.appspot.com/23471005

git-svn-id: svn://svn.chromium.org/blink/trunk@157246 bbb929c8-8fbe-4397-9dbb-9b2b20218538