Moves the instantiation of Cronet engine upstream.

Per @JensenPaul, instances of CronetEngine require a lot of resources. Creating
them is slow and expensive. For this reason, it's recommended to move the
creation of the engine up in the scope of the app to a longer-lived class.

This commit moves the creation of the engine to the activity level. The activity
also reuses a single instance of the class.

This commit also bumps the Cronet dependency to version 70.3538.110.

app/build.gradle

@@ -51,7 +51,7 @@ dependencies {
     implementation 'com.fasterxml.jackson.core:jackson-annotations:2.7.2'
     implementation 'com.fasterxml.jackson.core:jackson-databind:2.7.2'
     implementation 'com.android.support.constraint:constraint-layout:1.1.3'
-    implementation 'org.chromium.net:cronet-embedded:69.3497.100'
+    implementation 'org.chromium.net:cronet-embedded:70.3538.110'
 
     testImplementation 'junit:junit:4.12'
     androidTestImplementation 'com.android.support:support-annotations:28.0.0'

app/src/androidTest/java/com/google/cloud/solutions/flexenv/common/SpeechTranslationHelperAndroidTest.java

@@ -18,6 +18,7 @@
 import android.content.Context;
 import android.util.Log;
 
+import org.chromium.net.CronetEngine;
 import org.json.JSONException;
 import org.json.JSONObject;
 import org.junit.Assert;
@@ -38,6 +39,8 @@
 public class SpeechTranslationHelperAndroidTest {
     private static final String TAG = "SpeechTranslationHelperAndroidTest";
     private static String base64EncodedAudioMessage;
+    private static Context context;
+    private static CronetEngine cronetEngine;
 
     @Before
     public void readSpeechRecording16khzb64File() throws IOException {
@@ -53,17 +56,20 @@ public void readSpeechRecording16khzb64File() throws IOException {
             stringBuilder.append(line);
         }
         base64EncodedAudioMessage = stringBuilder.toString();
+
+        context = InstrumentationRegistry.getInstrumentation().getTargetContext();
+
+        CronetEngine.Builder myBuilder = new CronetEngine.Builder(context);
+        cronetEngine = myBuilder.build();
     }
 
     @Test
     public void translateAudioMessage_Success() throws InterruptedException {
         final Object waiter = new Object();
 
-        Context context = InstrumentationRegistry.getInstrumentation().getTargetContext();
-
         synchronized (waiter) {
             SpeechTranslationHelper.getInstance()
-                    .translateAudioMessage(context, base64EncodedAudioMessage,
+                    .translateAudioMessage(context, cronetEngine, base64EncodedAudioMessage,
                     16000, new SpeechTranslationHelper.SpeechTranslationListener() {
                         @Override
                         public void onTranslationSucceeded(String responseBody) {
@@ -99,11 +105,9 @@ public void onTranslationFailed(Exception e) {
     public void translateAudioMessage_Wrong_SampleRate() throws InterruptedException {
         final Object waiter = new Object();
 
-        Context context = InstrumentationRegistry.getInstrumentation().getTargetContext();
-
         synchronized (waiter) {
             SpeechTranslationHelper.getInstance()
-                    .translateAudioMessage(context, base64EncodedAudioMessage,
+                    .translateAudioMessage(context, cronetEngine, base64EncodedAudioMessage,
                             24000, new SpeechTranslationHelper.SpeechTranslationListener() {
                                 @Override
                                 public void onTranslationSucceeded(String responseBody) {

app/src/main/java/com/google/cloud/solutions/flexenv/PlayActivity.java

@@ -66,6 +66,7 @@
 import com.google.firebase.database.FirebaseDatabase;
 import com.google.firebase.database.ValueEventListener;
 
+import org.chromium.net.CronetEngine;
 import org.json.JSONException;
 import org.json.JSONObject;
 
@@ -112,6 +113,7 @@ public class PlayActivity
     private String currentChannel;
     private ChildEventListener channelListener;
     private SimpleDateFormat fmt;
+    private CronetEngine cronetEngine;
 
     private Menu channelMenu;
     private TextView channelLabel;
@@ -262,7 +264,8 @@ private void playMessage(String gcsBucket, String gcsPath) {
             mediaPlayer.start();
         } else {
             GcsDownloadHelper.getInstance().downloadGcsFile(
-                    getApplicationContext(), gcsBucket, gcsPath, new GcsDownloadHelper.GcsDownloadListener() {
+                    getApplicationContext(), getCronetEngine(), gcsBucket, gcsPath,
+                    new GcsDownloadHelper.GcsDownloadListener() {
                         @Override
                         public void onDownloadSucceeded(File file) {
                             MediaPlayer mediaPlayer = MediaPlayer.create(
@@ -342,6 +345,7 @@ public void onRecordingSucceeded(File output) {
                             base64EncodedAudioMessage = Base64EncodingHelper.encode(output);
                             SpeechTranslationHelper.getInstance().translateAudioMessage(
                                     getApplicationContext(),
+                                    getCronetEngine(),
                                     base64EncodedAudioMessage,
                                     16000,
                                     new SpeechTranslationHelper.SpeechTranslationListener() {
@@ -394,6 +398,21 @@ public void onRecordingFailed(Exception e) {
         }
     }
 
+    /**
+     * Creates an instance of the CronetEngine class.
+     * Instances of CronetEngine require a lot of resources. Additionally, their creation is slow
+     * and expensive. It's recommended to delay the creation of CronetEngine instances until they
+     * are required and reuse them as much as possible.
+     * @return An instance of CronetEngine.
+     */
+    private synchronized CronetEngine getCronetEngine() {
+        if(cronetEngine == null) {
+            CronetEngine.Builder myBuilder = new CronetEngine.Builder(this);
+            cronetEngine = myBuilder.build();
+        }
+        return cronetEngine;
+    }
+
     private void updateUI() {
         FirebaseUser currentUser = FirebaseAuth.getInstance().getCurrentUser();
         if (currentUser != null) {

app/src/main/java/com/google/cloud/solutions/flexenv/common/GcsDownloadHelper.java

@@ -66,11 +66,13 @@ public static GcsDownloadHelper getInstance() {
      * @param gcsPath The path of the object in the bucket.
      * @param downloadListener The callback to deliver the results to.
      */
-    public void downloadGcsFile(Context context, String gcsBucket, String gcsPath, GcsDownloadListener downloadListener) {
+    public void downloadGcsFile(Context context, CronetEngine cronetEngine, String gcsBucket,
+                                String gcsPath, GcsDownloadListener downloadListener) {
         getGcsAccessToken(context, new GcsTokenListener() {
             @Override
             public void onAccessTokenRequestSucceeded(String token) {
-                UrlRequest request = buildGcsRequest(context, gcsBucket, gcsPath, token,downloadListener);
+                UrlRequest request = buildGcsRequest(context, cronetEngine, gcsBucket, gcsPath,
+                        token, downloadListener);
                 request.start();
             }
             @Override
@@ -96,9 +98,9 @@ private void getGcsAccessToken(Context context, GcsTokenListener tokenListener)
         AsyncTask.execute(runnable);
     }
 
-    private UrlRequest buildGcsRequest(Context context, String gcsBucket, String gcsPath, String accessToken, GcsDownloadListener downloadListener) {
-        CronetEngine.Builder myBuilder = new CronetEngine.Builder(context);
-        CronetEngine cronetEngine = myBuilder.build();
+    private UrlRequest buildGcsRequest(Context context, CronetEngine cronetEngine, String gcsBucket,
+                                       String gcsPath, String accessToken,
+                                       GcsDownloadListener downloadListener) {
         Executor executor = Executors.newSingleThreadExecutor();
 
         String gcsPathEndpoint = context.getString(R.string.gcsBaseEndpoint) + gcsBucket + "/" + gcsPath;

app/src/main/java/com/google/cloud/solutions/flexenv/common/SpeechTranslationHelper.java

@@ -64,8 +64,8 @@ public static SpeechTranslationHelper getInstance() {
      * @param sampleRateInHertz The sample rate in hertz
      * @param translationListener The callback to deliver the results to.
      */
-    public void translateAudioMessage(Context context, String base64EncodedAudioMessage,
-                                      int sampleRateInHertz,
+    public void translateAudioMessage(Context context, CronetEngine cronetEngine,
+                                      String base64EncodedAudioMessage, int sampleRateInHertz,
                                       SpeechTranslationListener translationListener) {
         JSONObject requestBody = new JSONObject();
         try {
@@ -79,13 +79,13 @@ public void translateAudioMessage(Context context, String base64EncodedAudioMess
         }
 
         byte[] requestBodyBytes = requestBody.toString().getBytes();
-        UrlRequest request = buildSpeechTranslationRequest(context, requestBodyBytes, translationListener);
+        UrlRequest request = buildSpeechTranslationRequest(context, cronetEngine, requestBodyBytes, translationListener);
         request.start();
     }
 
-    private UrlRequest buildSpeechTranslationRequest(Context context, byte[] requestBody, SpeechTranslationListener translationListener) {
-        CronetEngine.Builder myBuilder = new CronetEngine.Builder(context);
-        CronetEngine cronetEngine = myBuilder.build();
+    private UrlRequest buildSpeechTranslationRequest(Context context, CronetEngine cronetEngine,
+                                                     byte[] requestBody,
+                                                     SpeechTranslationListener translationListener) {
         Executor executor = Executors.newSingleThreadExecutor();
         String speechTranslateEndpoint = context.getString(R.string.speechToSpeechEndpoint);
         UrlRequest.Builder requestBuilder = cronetEngine.newUrlRequestBuilder(