Fix crash if utterance is garbage-collected before speech ends.

Source/modules/speech/SpeechSynthesis.cpp

Index: Source/modules/speech/SpeechSynthesis.cpp
diff --git a/Source/modules/speech/SpeechSynthesis.cpp b/Source/modules/speech/SpeechSynthesis.cpp
index 00b60091d8d97ef02dbd8da2764236da39ca1907..d5b5608d6e26ef6985239cf939dd9b99d8a532b8 100644
--- a/Source/modules/speech/SpeechSynthesis.cpp
+++ b/Source/modules/speech/SpeechSynthesis.cpp
@@ -153,6 +153,10 @@ void SpeechSynthesis::handleSpeakingCompleted(SpeechSynthesisUtterance* utteranc
 {
     ASSERT(utterance);
 
+    // Keep the utterance around long enough to fire an event on it in case m_utteranceQueue
+    // is holding the last reference to it.
+    RefPtrWillBeRawPtr<SpeechSynthesisUtterance> protect(utterance);
+
     bool didJustFinishCurrentUtterance = false;
     // If the utterance that completed was the one we're currently speaking,
     // remove it from the queue and start speaking the next one.