Call JS functions via native context instead of js builtins object.

Call JS functions via native context instead of js builtins object.

We look up %-functions in the context if not found in the runtime.

R=bmeurer@chromium.org, mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/1306993003

Cr-Commit-Position: refs/heads/master@{#30379}