Previously, it was `ToString(PromiseCast)`, which comes out as
"function resolve() { [native code] }". I had changed it to "Promise.resolve()",
but the other style is more consistently used.

LOG=N
R=cbruni@chromium.org, adamk@chromium.org, littledan@chromium.org

Review URL: https://codereview.chromium.org/1560163002

Cr-Commit-Position: refs/heads/master@{#33129}