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This uses window.speechSynthesis, which should be using the TTS
engine and voice prefs selected by the user.

Bug: 823359
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I2b8cd29a2b1fd1da2a5cb002aeb877ed2e615196
Reviewed-on: https://chromium-review.googlesource.com/996764
Commit-Queue: Katie Dektar <katie@chromium.org>
Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Reviewed-by: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550199}