Add HttpUrlConnection backed implementation of CronetEngine.

components/cronet/android/api/src/org/chromium/net/CronetEngine.java

 // Copyright 2015 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.support.annotation.IntDef;
 import android.util.Log;
 
 import org.json.JSONArray;
 import org.json.JSONException;
 import org.json.JSONObject;
 
 import java.io.File;
+import java.io.IOException;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.lang.reflect.Constructor;
 import java.net.Proxy;
 import java.net.URL;
 import java.net.URLConnection;
 import java.net.URLStreamHandlerFactory;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.Executor;
@@ skipping 561 matching lines @@
 
     /**
      * Establishes a new connection to the resource specified by the {@link URL} {@code url}.
      * <p>
      * <b>Note:</b> Cronet's {@link java.net.HttpURLConnection} implementation is subject to certain
      * limitations, see {@link #createURLStreamHandlerFactory} for details.
      *
      * @param url URL of resource to connect to.
      * @return an {@link java.net.HttpURLConnection} instance implemented by this CronetEngine.
      */
-    public abstract URLConnection openConnection(URL url);
+    public abstract URLConnection openConnection(URL url) throws IOException;
 
     /**
      * Establishes a new connection to the resource specified by the {@link URL} {@code url}
      * using the given proxy.
      * <p>
      * <b>Note:</b> Cronet's {@link java.net.HttpURLConnection} implementation is subject to certain
      * limitations, see {@link #createURLStreamHandlerFactory} for details.
      *
      * @param url URL of resource to connect to.
      * @param proxy proxy to use when establishing connection.
      * @return an {@link java.net.HttpURLConnection} instance implemented by this CronetEngine.
      * @hide
      * @deprecated Marked as deprecated because @hide doesn't properly hide but
      *         javadocs are built with nodeprecated="yes".
      *         TODO(pauljensen): Expose once implemented, http://crbug.com/418111
      */
-    @SuppressWarnings("DepAnn") public abstract URLConnection openConnection(URL url, Proxy proxy);
+    @SuppressWarnings("DepAnn")
+    public abstract URLConnection openConnection(URL url, Proxy proxy) throws IOException;
 
     /**
      * Creates a {@link URLStreamHandlerFactory} to handle HTTP and HTTPS
      * traffic. An instance of this class can be installed via
      * {@link URL#setURLStreamHandlerFactory} thus using this CronetEngine by default for
      * all requests created via {@link URL#openConnection}.
      * <p>
      * Cronet does not use certain HTTP features provided via the system:
      * <ul>
      * <li>the HTTP cache installed via
@@ skipping 32 matching lines @@
     @Deprecated
     public static CronetEngine createContext(Builder builder) {
         CronetEngine cronetEngine = null;
         if (builder.getUserAgent().isEmpty()) {
             builder.setUserAgent(builder.getDefaultUserAgent());
         }
         if (!builder.legacyMode()) {
             cronetEngine = createCronetEngine(builder);
         }
         if (cronetEngine == null) {
-            // TODO(mef): Fallback to stub implementation. Once stub
-            // implementation is available merge with createCronetFactory.
-            cronetEngine = createCronetEngine(builder);
+            cronetEngine = new JavaCronetEngine(builder.getUserAgent());
         }
         Log.i(TAG, "Using network stack: " + cronetEngine.getVersionString());
         return cronetEngine;
     }
 
     private static CronetEngine createCronetEngine(Builder builder) {
         CronetEngine cronetEngine = null;
         try {
             Class<? extends CronetEngine> engineClass =
                     CronetEngine.class.getClassLoader()
                             .loadClass(CRONET_URL_REQUEST_CONTEXT)
                             .asSubclass(CronetEngine.class);
             Constructor<? extends CronetEngine> constructor =
                     engineClass.getConstructor(Builder.class);
             CronetEngine possibleEngine = constructor.newInstance(builder);
             if (possibleEngine.isEnabled()) {
                 cronetEngine = possibleEngine;
             }
         } catch (ClassNotFoundException e) {
             // Leave as null.
         } catch (Exception e) {
             throw new IllegalStateException("Cannot instantiate: " + CRONET_URL_REQUEST_CONTEXT, e);
         }
         return cronetEngine;
     }
 }