REGRESSION: Intermittent crash in SpeechSynthesis::didFinishSpeaking
https://bugs.webkit.org/show_bug.cgi?id=111613

Reviewed by Ryosuke Niwa.

This crash happens when the mock synthesizer utterance variable gets cleared
before the speakingFinished timer happens. I don't see how that could happen
but I was able to make a similar problem happen when cancel is called twice.

This adds in a few more asserts and common sense checks. I'm hoping it will
illuminate the problem further.

* platform/mock/PlatformSpeechSynthesizerMock.cpp:
(WebCore::PlatformSpeechSynthesizerMock::speakingFinished):
(WebCore::PlatformSpeechSynthesizerMock::speak):
(WebCore::PlatformSpeechSynthesizerMock::cancel):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@145304 268f45cc-cd09-0410-ab3c-d52691b4dbfc