Make TTS stop when switching screens in companion

Change-Id: I993a7b73eee00b3469626c6b78369570e387d821

appinventor/components/src/com/google/appinventor/components/runtime/TextToSpeech.java

@@ -69,7 +69,7 @@ description = "The TextToSpeech component speaks a given text aloud.  You can se
     iconName = "images/textToSpeech.png")
 @SimpleObject
 public class TextToSpeech extends AndroidNonvisibleComponent
-implements Component, OnStopListener, OnResumeListener, OnDestroyListener /*, ActivityResultListener  */{
+    implements Component, OnStopListener, OnResumeListener, OnDestroyListener, OnClearListener {
 
   private static final Map<String, Locale> iso3LanguageToLocaleMap = Maps.newHashMap();
   private static final Map<String, Locale> iso3CountryToLocaleMap = Maps.newHashMap();
@@ -487,4 +487,8 @@ implements Component, OnStopListener, OnResumeListener, OnDestroyListener /*, Ac
     tts.onDestroy();
   }
 
+  @Override
+  public void onClear() {
+    tts.onDestroy();
+  }
 }