Fix flaky NQE QUIC test

components/cronet/android/test/javatests/src/org/chromium/net/TestNetworkQualityRttListener.java

Index: components/cronet/android/test/javatests/src/org/chromium/net/TestNetworkQualityRttListener.java
diff --git a/components/cronet/android/test/javatests/src/org/chromium/net/TestNetworkQualityRttListener.java b/components/cronet/android/test/javatests/src/org/chromium/net/TestNetworkQualityRttListener.java
index afeec1f4f53651b45986b50ca842f4fbe79115b2..c2a937ea25d14092651545b9e006c1c4575051d6 100644
--- a/components/cronet/android/test/javatests/src/org/chromium/net/TestNetworkQualityRttListener.java
+++ b/components/cronet/android/test/javatests/src/org/chromium/net/TestNetworkQualityRttListener.java
@@ -6,6 +6,7 @@ package org.chromium.net;
 
 import static junit.framework.Assert.assertEquals;
 
+import android.os.ConditionVariable;
 import android.util.SparseIntArray;
 
 import java.util.concurrent.Executor;
@@ -13,6 +14,10 @@ import java.util.concurrent.Executor;
 class TestNetworkQualityRttListener extends NetworkQualityRttListener {
     // Lock to ensure that observation counts can be updated and read by different threads.
     private final Object mLock = new Object();
+
+    // Signals when the first RTT observation at the URL request layer is received.
+    private final ConditionVariable mWaitForUrlRequestRtt = new ConditionVariable();
+
     private int mRttObservationCount;
 
     // Holds the RTT observations counts indexed by source.
@@ -20,6 +25,11 @@ class TestNetworkQualityRttListener extends NetworkQualityRttListener {
 
     private Thread mExecutorThread;
 
+    /*
+     * Constructs a NetworkQualityRttListener that can listen to the RTT observations at various
+     * layers of the network stack.
+     * @param executor The executor on which the observations are reported.
+     */
     TestNetworkQualityRttListener(Executor executor) {
         super(executor);
     }
@@ -27,6 +37,11 @@ class TestNetworkQualityRttListener extends NetworkQualityRttListener {
     @Override
     public void onRttObservation(int rttMs, long when, int source) {
         synchronized (mLock) {
+            if (source == 0) {
+                // Source 0 indicates that the RTT was observed at the URL request layer.
+                mWaitForUrlRequestRtt.open();
+            }
+
             mRttObservationCount++;
             mRttObservationCountBySource.put(source, mRttObservationCountBySource.get(source) + 1);
 
@@ -38,6 +53,13 @@ class TestNetworkQualityRttListener extends NetworkQualityRttListener {
         }
     }
 
+    /*
+     * Blocks until the first RTT observation at the URL request layer is received.
+     */
+    public void waitUntilFirstUrlRequestRTTReceived() {
+        mWaitForUrlRequestRtt.block();
+    }
+
     public int rttObservationCount() {
         synchronized (mLock) {
             return mRttObservationCount;