Extend PlatformSpeechSynthesizerMock with an utterance queue.

Source/modules/speech/testing/PlatformSpeechSynthesizerMock.h

Index: Source/modules/speech/testing/PlatformSpeechSynthesizerMock.h
diff --git a/Source/modules/speech/testing/PlatformSpeechSynthesizerMock.h b/Source/modules/speech/testing/PlatformSpeechSynthesizerMock.h
index 8c36f9b53bb0fa85b529611ea017c83497c65fdf..5d4d36dd7edd0189ecf0d161b5569a4a11c8eec5 100644
--- a/Source/modules/speech/testing/PlatformSpeechSynthesizerMock.h
+++ b/Source/modules/speech/testing/PlatformSpeechSynthesizerMock.h
@@ -36,23 +36,30 @@ class PlatformSpeechSynthesizerMock final : public PlatformSpeechSynthesizer {
 public:
     static PlatformSpeechSynthesizerMock* create(PlatformSpeechSynthesizerClient*);
 
-    virtual ~PlatformSpeechSynthesizerMock();
-    virtual void speak(PlatformSpeechSynthesisUtterance*) override;
-    virtual void pause() override;
-    virtual void resume() override;
-    virtual void cancel() override;
+    ~PlatformSpeechSynthesizerMock() override;
+    void speak(PlatformSpeechSynthesisUtterance*) override;
+    void pause() override;
+    void resume() override;
+    void cancel() override;
 
-    virtual void trace(Visitor*) override;
+    void trace(Visitor*) override;
 
 private:
     explicit PlatformSpeechSynthesizerMock(PlatformSpeechSynthesizerClient*);
-    virtual void initializeVoiceList() override;
-    void speakingFinished(Timer<PlatformSpeechSynthesizerMock>*);
+
+    void initializeVoiceList() override;
+
+    void speakNext();
+    void speakNow();
+
     void speakingErrorOccurred(Timer<PlatformSpeechSynthesizerMock>*);
+    void speakingFinished(Timer<PlatformSpeechSynthesizerMock>*);
 
-    Timer<PlatformSpeechSynthesizerMock> m_speakingFinishedTimer;
     Timer<PlatformSpeechSynthesizerMock> m_speakingErrorOccurredTimer;
-    Member<PlatformSpeechSynthesisUtterance> m_utterance;
+    Timer<PlatformSpeechSynthesizerMock> m_speakingFinishedTimer;
+
+    Member<PlatformSpeechSynthesisUtterance> m_currentUtterance;
+    HeapDeque<Member<PlatformSpeechSynthesisUtterance>> m_queuedUtterances;
 };
 
 } // namespace blink