[Kiosk] Reset the configration of tts preferences

During profile startup, some of the a11y preferences were not reset --
those related to the mutualof tts engines used by extensions. Here
we reset them as well.

Bug: 1049566
Change-Id: If4c57cc3a165871eaa812af58e6d698c25be36e2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2360018Reviewed-by: Anqing Zhao <anqing@chromium.org>
Commit-Queue: Anatoliy Potapchuk <apotapchuk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#799060}

chrome/browser/chromeos/app_mode/app_launch_utils.cc

@@ -20,7 +20,8 @@ namespace {
 
 // The list of prefs that are reset on the start of each kiosk session.
 const char* const kPrefsToReset[] = {"settings.accessibility",  // ChromeVox
-                                     "settings.a11y", "ash.docked_magnifier"};
+                                     "settings.a11y", "ash.docked_magnifier",
+                                     "settings.tts"};
 
 // This vector is used in tests when they want to replace |kPrefsToReset| with
 // their own list.