Fix flaky NQE cronet test

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

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.net;
 
 import static org.chromium.base.CollectionUtil.newHashSet;
 
 import android.content.Context;
 import android.content.ContextWrapper;
@@ skipping 264 matching lines @@
     // TODO(xunjieli): Remove annotation after crbug.com/539519 is fixed.
     @SuppressWarnings("deprecation")
     public void testRealTimeNetworkQualityObservations() throws Exception {
         mTestFramework = startCronetTestFramework();
         TestExecutor testExecutor = new TestExecutor();
         TestNetworkQualityListener networkQualityListener = new TestNetworkQualityListener();
         mTestFramework.mCronetEngine.enableNetworkQualityEstimatorForTesting(
                 true, true, testExecutor);
         mTestFramework.mCronetEngine.addRttListener(networkQualityListener);
         mTestFramework.mCronetEngine.addThroughputListener(networkQualityListener);
-        TestUrlRequestCallback callback = new TestUrlRequestCallback();
-        UrlRequest urlRequest =
-                mTestFramework.mCronetEngine.createRequest(mUrl, callback, callback.getExecutor());
-        urlRequest.start();
-        callback.blockForDone();
-        testExecutor.runAllTasks();
+
+        // Throughput observation is posted to network quality estimator, and running two requests

[xunjieli, 2016/05/24 01:54:43]

The comment is a little vague, and I don't quite understand why starting a
second request forces the NQE throughput callback to be flushed.
When will we know the throughput observation of the first request ? Will it
definitely occur before the second request?

[tbansal1, 2016/05/24 16:57:08]

I updated the comment. Let me know if it is still confusing. 

+        // ensures that the observation corresponding to the first request is posted in time.
+        for (int i = 0; i < 2; ++i) {
+            TestUrlRequestCallback callback = new TestUrlRequestCallback();
+            UrlRequest urlRequest = mTestFramework.mCronetEngine.createRequest(
+                    mUrl, callback, callback.getExecutor());
+            urlRequest.start();
+            callback.blockForDone();
+            testExecutor.runAllTasks();
+        }
+
         assertTrue(networkQualityListener.rttObservationCount() > 0);
         assertTrue(networkQualityListener.throughputObservationCount() > 0);
         mTestFramework.mCronetEngine.shutdown();
     }
 
     private static class TestRequestFinishedListener
             implements CronetEngine.RequestFinishedListener {
         private UrlRequestInfo mRequestInfo = null;
 
         @Override
@@ skipping 845 matching lines @@
                     }
                 }.start();
                 otherThreadDone.block();
                 builder.build().shutdown();
                 uiThreadDone.open();
             }
         });
         assertTrue(uiThreadDone.block(1000));
     }
 }