Previously API function calls would only be optimized in TurboFan when
the receiver was a (compile-time) known constant, which was probably
only true for certain cases where functions where called on the global
proxy (the window object).

BUG=v8:5267,v8:6304
R=jarin@chromium.org

Review-Url: https://codereview.chromium.org/2839953002
Cr-Commit-Position: refs/heads/master@{#44877}