Updates TTS javascript with Google3 version.

This brings the Google3 and ChromeOS versions of the TTS
javascript extension to the same place. In cl/187193272,
the Chrome OS versions (here) were pushed to Google3, and
this backports changes made due to style or comments.

TEST=Tried running the extension locally using this JS
BUG=None
Change-Id: I124ed296b325ad9a465b78c31720527ab8cbc3b2
Reviewed-on: https://chromium-review.googlesource.com/940270
Commit-Ready: Katie Dektar <katie@chromium.org>
Tested-by: Katie Dektar <katie@chromium.org>
Reviewed-by: Katie Dektar <katie@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
2 files changed