Always print external time in --trace-gc to make it toolable.
Always print external time in --trace-gc to make it toolable.

BUG=

Review URL: https://codereview.chromium.org/1173243003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#28939}

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