blink: fix minor misspelling.

BUG=none
TEST=none

Change-Id: If82677ec23c81f8051a86a9286c6b64e34d7a22d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2255309
Auto-Submit: Scott Violet <sky@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#781273}

third_party/blink/public/mojom/speech/speech_synthesis.mojom

@@ -26,7 +26,7 @@ struct SpeechSynthesisVoice {
   bool is_default;
 };
 
-// This interface receives updates to the list of voices. See SpeechSythesis'
+// This interface receives updates to the list of voices. See SpeechSynthesis'
 // AddVoiceListObserver method.
 interface SpeechSynthesisVoiceListObserver {
   // Receives the list of voices that may be used.