This CL applies the same optimization already present for calling API-function.
Execution::New and Execution::Call now both check whether the target is an
API-function and avoid calling out into the construct/call stub.

BUG=chromium:630217

Review-Url: https://codereview.chromium.org/2203353002
Cr-Commit-Position: refs/heads/master@{#38433}