Enable NQE when Cronet Engine is built

components/cronet/android/api/src/org/chromium/net/NetworkQualityThroughputListener.java

Index: components/cronet/android/api/src/org/chromium/net/NetworkQualityThroughputListener.java
diff --git a/components/cronet/android/api/src/org/chromium/net/NetworkQualityThroughputListener.java b/components/cronet/android/api/src/org/chromium/net/NetworkQualityThroughputListener.java
index 196dbeccb2d7389599b04852c6d49cc54202924f..44caac8987b5e63cb350e9f081e8a9cc1a57de3e 100644
--- a/components/cronet/android/api/src/org/chromium/net/NetworkQualityThroughputListener.java
+++ b/components/cronet/android/api/src/org/chromium/net/NetworkQualityThroughputListener.java
@@ -4,16 +4,39 @@
 
 package org.chromium.net;
 
+import java.util.concurrent.Executor;
+
 /**
- * Interface to watch for observations of throughput.
+ * Listener that is notified of throughput observations from the network quality
+ * estimator.
  * {@hide} as it's a prototype.
  */
-public interface NetworkQualityThroughputListener {
+public abstract class NetworkQualityThroughputListener {
+    /**
+     * The executor on which this listener will be notified. Set as a final
+     * field, so it can be safely accessed across threads.
+     */
+    private final Executor mExecutor;
+
+    /**
+     * @param executor The executor on which the observations are reported.
+     */
+    public NetworkQualityThroughputListener(Executor executor) {
+        if (executor == null) {
+            throw new IllegalStateException("Executor must not be null");
+        }
+        mExecutor = executor;
+    }
+
+    public Executor getExecutor() {
+        return mExecutor;
+    }
+
     /**
      * Reports a new throughput observation.
      * @param throughputKbps the downstream throughput in kilobits per second.
      * @param whenMs milliseconds since the Epoch (January 1st 1970, 00:00:00.000).
      * @param source the observation source from {@link NetworkQualityObservationSource}.
      */
-    public void onThroughputObservation(int throughputKbps, long whenMs, int source);
+    public abstract void onThroughputObservation(int throughputKbps, long whenMs, int source);
 }