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Web Speech API [1] consists of two parts:
1. speech recognition (speech-to-text, STT)
2. speech synthesis (text-to-speech, TTS)

Currently Web Speech API can be either enabled or disabled completely,
by means of "disable-speech-api" command line flag. However we want to
be able to enable STT and TTS functionality separately. This has to do
with some security/privacy concerns regarding speech synthesis.

In particular we want to enable STT functionality in Android WebView,
but not TTS (at least until all concerns are addressed).

In this patch the ScriptedSpeech runtime blink flag is split into two:
ScriptedSpeechRecognition and ScriptedSpeechSynthesis. An additional
"disable-speech-synthesis-api" command line flag is added to control
how much of the Web Speech API we want to expose.

[1] https://w3c.github.io/speech-api/

BUG=487255

Change-Id: I959b73600bb8e7a0542661bfb997ceae1aa144ed
Reviewed-on: https://chromium-review.googlesource.com/c/1329150
Commit-Queue: Tim Volodine <timvolodine@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608374}