Enable NQE when Cronet Engine is built

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

Index: components/cronet/android/api/src/org/chromium/net/NetworkQualityRttListener.java
diff --git a/components/cronet/android/api/src/org/chromium/net/NetworkQualityRttListener.java b/components/cronet/android/api/src/org/chromium/net/NetworkQualityRttListener.java
index cd04f6ebfcca635cbaba2f0d9888c2aae6c7d383..4eb87307fdc460caaa6b5b0a0203f4df7ec3f52f 100644
--- a/components/cronet/android/api/src/org/chromium/net/NetworkQualityRttListener.java
+++ b/components/cronet/android/api/src/org/chromium/net/NetworkQualityRttListener.java
@@ -4,19 +4,50 @@
 
 package org.chromium.net;
 
+import java.util.concurrent.Executor;
+
 /**
- * Interface to watch for observations of various round trip times (RTTs) at
- * various layers of the network stack. These include RTT estimates by QUIC
- * and TCP, as well as the time between when a URL request is sent and when
- * the first byte of the response is received.
+ * Watches observations of various round trip times (RTTs) at various layers of
+ * the network stack. These include RTT estimates by QUIC and TCP, as well as
+ * the time between when a URL request is sent and when the first byte of the
+ * response is received.
  * {@hide} as it's a prototype.
  */
-public interface NetworkQualityRttListener {
+public abstract class NetworkQualityRttListener {
+    /**
+     * 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;
+
+    // TODO(tbansal):  http://crbug.com/618034 Remove this constructor.
+    public NetworkQualityRttListener() {
+        mExecutor = null;
+    }
+
+    /**
+     * @param executor The executor on which the observations are reported.
+     */
+    public NetworkQualityRttListener(Executor executor) {
+        // TODO(tbansal):  http://crbug.com/618034 Uncomment this block, once
+        // all embedders start providing a non-null executor.

[mef, 2016/06/20 16:50:27]

Wouldn't existing embedders use default constructor? 
Can we enable the check now?

[tbansal1, 2016/06/20 20:06:57]

Good point. Done. I had to modify the test code a little bit.

+        /*
+        if (executor == null) {
+            throw new IllegalStateException("Executor must not be null");
+        }
+        */
+        mExecutor = executor;
+    }
+
+    public Executor getExecutor() {
+        return mExecutor;
+    }
+
     /**
      * Reports a new round trip time observation.
      * @param rttMs the round trip time in milliseconds.
      * @param whenMs milliseconds since the Epoch (January 1st 1970, 00:00:00.000).
      * @param source the observation source from {@link NetworkQualityObservationSource}.
      */
-    public void onRttObservation(int rttMs, long whenMs, int source);
+    public abstract void onRttObservation(int rttMs, long whenMs, int source);
 }