The CallApiCallbackStub can avoid loading undefined in case the
call_data is already undefined, which doubles the number of versions of
the stub and adds unnecessary complexity (at the benefit of saving one
stupid load). The idea is to turn the CallApiCallbackStub into a single
builtin instead, which does the right thing, so this is the first step
towards that goal.

R=yangguo@chromium.org
BUG=v8:6304

Review-Url: https://codereview.chromium.org/2838143003
Cr-Commit-Position: refs/heads/master@{#44869}