Expose the currently used engine to bundled apps.

This is required to fix a couple of niggles and annoyances
in the Settings app.

Change-Id: I0ad0c41744282b552e844ba9a2157cea74c64234

core/java/android/speech/tts/TextToSpeech.java

@@ -442,7 +442,7 @@ public class TextToSpeech {
     private final Map<String, Uri> mUtterances;
     private final Bundle mParams = new Bundle();
     private final TtsEngines mEnginesHelper;
-    private String mCurrentEngine = null;
+    private volatile String mCurrentEngine = null;
 
     /**
      * The constructor for the TextToSpeech class, using the default TTS engine.
@@ -573,6 +573,7 @@ public class TextToSpeech {
                 service.setCallback(getPackageName(), null);
                 service.stop(getPackageName());
                 mServiceConnection.disconnect();
+                mCurrentEngine = null;
                 return null;
             }
         }, null, "shutdown");
@@ -868,6 +869,14 @@ public class TextToSpeech {
         return ERROR;
     }
 
+    /**
+     * @return the engine currently in use by this TextToSpeech instance.
+     * @hide
+     */
+    public String getCurrentEngine() {
+        return mCurrentEngine;
+    }
+
     /**
      * Sets the text-to-speech language.
      * The TTS engine will try to use the closest match to the specified