AshBrowserTestStarter: HasLacrosArgument is const

HasLacrosArgument() if often the only AshBrowserTestStarter method
used in test bodies. Such tests now only need const reference
access to the AshBrowserTestStarter.

Change-Id: Iefe69c0e6de5934c6f1623378f20111403300609
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3695640
Commit-Queue: Sven Zheng <svenzheng@chromium.org>
Auto-Submit: Eric Willigers <ericwilligers@chromium.org>
Reviewed-by: Sven Zheng <svenzheng@chromium.org>
Commit-Queue: Eric Willigers <ericwilligers@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1012282}