Since we don't create an AllocationSite for the empty object literal, the
TF lowering bailed out early and used the slow runtime call as a fallback.

Bug: chromium:757596, v8:6211
Change-Id: I68307ff2d0870c35f07c3aad4cd10cf08e378686
Reviewed-on: https://chromium-review.googlesource.com/625619Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47514}