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

components/cronet/android/java/src/org/chromium/net/CronetUrlRequestContext.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.os.Build;
 import android.os.ConditionVariable;
 import android.os.Handler;
@@ skipping 58 matching lines @@
 
     @GuardedBy("mNetworkQualityLock")
     private final ObserverList<NetworkQualityThroughputListener> mThroughputListenerList =
             new ObserverList<NetworkQualityThroughputListener>();
 
     @GuardedBy("mNetworkQualityLock")
     private final ObserverList<RequestFinishedListener> mFinishedListenerList =
             new ObserverList<RequestFinishedListener>();
 
     @UsedByReflection("CronetEngine.java")
-    public CronetUrlRequestContext(CronetEngine.Builder builder) {
+    public CronetUrlRequestContext(final CronetEngine.Builder builder) {
         CronetLibraryLoader.ensureInitialized(builder.getContext(), builder);
         nativeSetMinLogLevel(getLoggingLevel());
         synchronized (mLock) {
             mUrlRequestContextAdapter = nativeCreateRequestContextAdapter(
                     createNativeUrlRequestContextConfig(builder.getContext(), builder));
             if (mUrlRequestContextAdapter == 0) {
                 throw new NullPointerException("Context Adapter creation failed.");
             }
         }
 
         // Init native Chromium URLRequestContext on main UI thread.
         Runnable task = new Runnable() {
             @Override
             public void run() {
+                CronetLibraryLoader.ensureMainThreadInitialized(builder.getContext());
                 synchronized (mLock) {
                     // mUrlRequestContextAdapter is guaranteed to exist until
                     // initialization on main and network threads completes and
                     // initNetworkThread is called back on network thread.
                     nativeInitRequestContextOnMainThread(mUrlRequestContextAdapter);
                 }
             }
         };
         // Run task immediately or post it to the UI thread.
         if (Looper.getMainLooper() == Looper.myLooper()) {
@@ skipping 401 matching lines @@
     @NativeClassQualifiedName("CronetURLRequestContextAdapter")
     private native void nativeEnableNetworkQualityEstimator(
             long nativePtr, boolean useLocalHostRequests, boolean useSmallerResponses);
 
     @NativeClassQualifiedName("CronetURLRequestContextAdapter")
     private native void nativeProvideRTTObservations(long nativePtr, boolean should);
 
     @NativeClassQualifiedName("CronetURLRequestContextAdapter")
     private native void nativeProvideThroughputObservations(long nativePtr, boolean should);
 }