Install SODA for headless captioning.

Previously, the SODA installer didn't check if the headless
captioning pref was set, so it wouldn't install SODA.  This has a
potentially significant detrimental effect on both the objective
efficacy and accuracy of headless captioning, and also it doesn't
work at all.

Bug: 410644442, 419829498
Change-Id: I52fd7feb51e32b2ed495c49aac2fc107387b669b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6594496
Reviewed-by: Evan Liu <evliu@google.com>
Reviewed-by: Abigail Klein <abigailbklein@google.com>
Auto-Submit: Frank Liberato <liberato@chromium.org>
Commit-Queue: Frank Liberato <liberato@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1467723}