Don't overwrite existing serial numbers on the function template, otherwise instantiating the function for a new context causes the serial number to bump.
Don't overwrite existing serial numbers on the function template, otherwise instantiating the function for a new context causes the serial number to bump.

Review URL: https://codereview.chromium.org/988693003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#27048}

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh