[Cronet] Avoid crashing when CronetEngines are created on multiple threads

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 1107 matching lines @@
         builder.setLibraryLoader(loader).setLibraryName("cronet_tests");
         try {
             // ensureInitialized() calls native code to check the version right after library load
             // and will error with the message below if library loading was skipped
             CronetLibraryLoader.ensureInitialized(getContext(), builder);
             fail("Native library should not be loaded");
         } catch (UnsatisfiedLinkError e) {
             assertTrue(loader.wasCalled());
         }
     }
+
+    // Creates a CronetEngine on another thread and then one on the main thread.  This shouldn't
+    // crash.
+    @SmallTest
+    @Feature({"Cronet"})
+    public void testThreadedStartup() throws Exception {
+        final ConditionVariable otherThreadDone = new ConditionVariable();
+        final ConditionVariable uiThreadDone = new ConditionVariable();
+        new Handler(Looper.getMainLooper()).post(new Runnable() {
+            public void run() {
+                final CronetEngine.Builder builder =
+                        new CronetEngine.Builder(getContext()).setLibraryName("cronet_tests");
+                new Thread() {
+                    public void run() {
+                        CronetEngine cronetEngine = builder.build();

[mef, 2016/04/27 18:48:15]

Can we create and start a new request here, before opening otherThreadDone?
If I understand Andrei's concern, there is a good chance of running into issues
here because library is still not initialized.

[pauljensen, 2016/04/27 19:04:24]

We could do lots of things here.  I think our other tests cover creating a
CronetEngine and UrlRequests on a non-main thread quite well.  This test
triggers the crash I'm concerned with.

[mef, 2016/04/27 19:50:00]

Acknowledged.

+                        otherThreadDone.open();
+                        cronetEngine.shutdown();
+                    }
+                }.start();
+                otherThreadDone.block();

[mef, 2016/04/27 18:48:15]

OTOH I can see Paul's point that this will deadlock if otherThread would wait
for init to complete on main thread.

+                builder.build().shutdown();
+                uiThreadDone.open();
+            }
+        });
+        assertTrue(uiThreadDone.block(1000));
+    }
 }