Updating trunk VERSION from 4877.0 to 4878.0

* This is an automated release commit.
* Do not revert without consulting chrome-pmo@google.com.
NOAUTOREVERT=true

Change-Id: I896c74ea80338edd163e7c673c9d9641171383da
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3448431
Bot-Commit: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#968344}