Extend PlatformSpeechSynthesizerMock with an utterance queue.

Source/modules/speech/SpeechRecognitionResult.cpp

Index: Source/modules/speech/SpeechRecognitionResult.cpp
diff --git a/Source/modules/speech/SpeechRecognitionResult.cpp b/Source/modules/speech/SpeechRecognitionResult.cpp
index 7e856174d948422948f13d681fe98df837dd364f..38f3c55242f2b4b585c67577d1f78fb87b431359 100644
--- a/Source/modules/speech/SpeechRecognitionResult.cpp
+++ b/Source/modules/speech/SpeechRecognitionResult.cpp
@@ -37,9 +37,9 @@ SpeechRecognitionResult* SpeechRecognitionResult::create(const HeapVector<Member
 SpeechRecognitionAlternative* SpeechRecognitionResult::item(unsigned index)
 {
     if (index >= m_alternatives.size())
-        return 0;
+        return nullptr;
 
-    return m_alternatives[index].get();
+    return m_alternatives[index];
 }
 
 SpeechRecognitionResult::SpeechRecognitionResult(const HeapVector<Member<SpeechRecognitionAlternative>>& alternatives, bool final)