The promise constructor fast-path did allocate contexts that were
too large, resulting in GC overhead compared to the slow-path which
contributes to a performance regression we are currently dealing with.

Bug: chromium:829253
Change-Id: I82883358933df9ce5241bad53b85867455046cc1
Reviewed-on: https://chromium-review.googlesource.com/1007054Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52550}