Add SpeechSynthesisErrorEvent to not-webview-exposed.txt

Web Speech API is not implemented on WebView.

Bug: 890499
Change-Id: I0f8e94c5662f7213ff1d5ce5e13dbcab515bed66
Reviewed-on: https://chromium-review.googlesource.com/1254466Reviewed-by: Tim Volodine <timvolodine@chromium.org>
Commit-Queue: Charlie Harrison <csharrison@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595455}

android_webview/tools/system_webview_shell/test/data/webexposed/not-webview-exposed.txt

 # speech api not enabled in webview, crbug.com/487255
+interface SpeechSynthesisErrorEvent : SpeechSynthesisEvent
 interface SpeechSynthesisEvent : Event
 interface SpeechSynthesisUtterance : EventTarget
 interface webkitSpeechGrammar