Fix missing check for ChromeVoxState.instance before use

If enableSpeechLogging is changed to true by default,
this routine is called before ChromeVoxState.instance is
initialized.  Adding a check to prevent the exception.

Bug: None
Test: Manual
Change-Id: I41af3fb914d13a60ec6b8a256faa626ff6444bd1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1651037
Reviewed-by: Alice Boxhall <aboxhall@chromium.org>
Commit-Queue: Randy Rossi <rmrossi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#669333}
1 file changed