[Cronet] Regression test for DCHECK when histograms read on another thread

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 android.content.Context;
 import android.content.ContextWrapper;
 import android.os.ConditionVariable;
 import android.os.Handler;
@@ skipping 1127 matching lines @@
         firstEngine.shutdown();
         secondEngine.shutdown();
         thirdEngine.shutdown();
     }
 
     @SmallTest
     @Feature({"Cronet"})
     public void testGetGlobalMetricsDeltas() throws Exception {
         final CronetTestFramework testFramework = startCronetTestFramework();
 
-        byte delta1[] = testFramework.mCronetEngine.getGlobalMetricsDeltas();
+        final byte delta1[] = testFramework.mCronetEngine.getGlobalMetricsDeltas();
 
-        TestUrlRequestCallback callback = new TestUrlRequestCallback();
+        final TestUrlRequestCallback callback = new TestUrlRequestCallback();
         UrlRequest.Builder builder = testFramework.mCronetEngine.newUrlRequestBuilder(
                 mUrl, callback, callback.getExecutor());
         builder.build().start();
-        callback.blockForDone();
-        byte delta2[] = testFramework.mCronetEngine.getGlobalMetricsDeltas();
-        assertTrue(delta2.length != 0);
-        assertFalse(Arrays.equals(delta1, delta2));
+        // Fetch deltas on a different thread the second time to make sure this is permitted.
+        // See crbug.com/719448
+        final ConditionVariable cv = new ConditionVariable();
+        new Thread(new Runnable() {
+            @Override
+            public void run() {
+                callback.blockForDone();
+                byte delta2[] = testFramework.mCronetEngine.getGlobalMetricsDeltas();
+                assertTrue(delta2.length != 0);

[mef, 2017/05/09 15:13:26]

AFAIK JUnit assertions only work properly on the main test thread. 
Can we collect delta2 on worker thread, but perform asserts after cv.block()?

[pauljensen, 2017/05/09 15:55:54]

Done.

+                assertFalse(Arrays.equals(delta1, delta2));
+                cv.open();
+            }
+        })
+                .start(); // TODO(pauljensen): weird spaces crbug.com/719964
+        cv.block();
     }
 
     @SmallTest
     @Feature({"Cronet"})
     public void testCronetEngineBuilderConfig() throws Exception {
         // This is to prompt load of native library.
         startCronetTestFramework();
         // Verify CronetEngine.Builder config is passed down accurately to native code.
         ExperimentalCronetEngine.Builder builder =
                 new ExperimentalCronetEngine.Builder(getContext());
@@ skipping 92 matching lines @@
         TestUrlRequestCallback callback = new TestUrlRequestCallback();
         URL requestUrl =
                 new URL("http", resolverTestHostname, testUrl.getPort(), testUrl.getFile());
         UrlRequest.Builder urlRequestBuilder = testFramework.mCronetEngine.newUrlRequestBuilder(
                 requestUrl.toString(), callback, callback.getExecutor());
         urlRequestBuilder.build().start();
         callback.blockForDone();
         assertEquals(200, callback.mResponseInfo.getHttpStatusCode());
     }
 }