GitLab

Make CreateExtension use the semantic ExtensionBuilder to cut down on
boilerplate.

Bug: None
Change-Id: I19fc5c74efc7f67145e9f14b445bdeb66ca933c2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1896390Reviewed-by: Caroline Rising <corising@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#712760}