Separate LazyBrowserInterfaceBroker from LoadAllTabsAtStartup.

- LoadAllTabsAtStartup is unlikely to launch in the near term.
- LazyBrowserInterfaceBroker should be safe to launch on all platforms.

Change-Id: Ic58bc105004f47a40b63afa99848861f183f51d9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7711935
Auto-Submit: Calder Kitagawa <ckitagawa@chromium.org>
Reviewed-by: Brandon Wylie <wylieb@google.com>
Commit-Queue: Calder Kitagawa <ckitagawa@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1607202}
NOKEYCHECK=True
GitOrigin-RevId: f1673055577dcf95be3fb4e78f92877cb51cb46a