Add HttpUrlConnection backed implementation of CronetEngine.

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

Index: components/cronet/android/api/src/org/chromium/net/JavaCronetEngine.java
diff --git a/components/cronet/android/api/src/org/chromium/net/JavaCronetEngine.java b/components/cronet/android/api/src/org/chromium/net/JavaCronetEngine.java
new file mode 100644
index 0000000000000000000000000000000000000000..4fbe1c9cb03d0fd048e1a1a5063614fa6b8cea5c
--- /dev/null
+++ b/components/cronet/android/api/src/org/chromium/net/JavaCronetEngine.java
@@ -0,0 +1,141 @@
+// 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 static android.os.Process.THREAD_PRIORITY_BACKGROUND;
+import static android.os.Process.THREAD_PRIORITY_MORE_FAVORABLE;
+
+import java.io.IOException;
+import java.net.Proxy;
+import java.net.URL;
+import java.net.URLConnection;
+import java.net.URLStreamHandler;
+import java.net.URLStreamHandlerFactory;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.Executor;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ThreadFactory;
+
+/**
+ * {@link java.net.HttpURLConnection} backed CronetEngine.
+ *
+ * <p>Does not support netlogs, transferred data measurement, bidistream, cache, or priority.
+ */
+final class JavaCronetEngine extends CronetEngine {
+    private final String mUserAgent;
+
+    private final ExecutorService mExecutorService =
+            Executors.newCachedThreadPool(new ThreadFactory() {
+                @Override
+                public Thread newThread(final Runnable r) {
+                    return Executors.defaultThreadFactory().newThread(new Runnable() {
+                        @Override
+                        public void run() {
+                            Thread.currentThread().setName("JavaCronetEngine");
+                            // On android, all background threads (and all threads that are part
+                            // of background processes) are put in a cgroup that is allowed to
+                            // consume up to 5% of CPU - these worker threads spend the vast
+                            // majority of their time waiting on I/O, so making them contend with
+                            // background applications for a slice of CPU doesn't make much sense.
+                            // We want to hurry up and get idle.
+                            android.os.Process.setThreadPriority(
+                                    THREAD_PRIORITY_BACKGROUND + THREAD_PRIORITY_MORE_FAVORABLE);
+                            r.run();
+                        }
+                    });
+                }
+            });
+
+    JavaCronetEngine(String userAgent) {
+        this.mUserAgent = userAgent;
+    }
+
+    @Override
+    public UrlRequest createRequest(String url, UrlRequest.Callback callback, Executor executor) {
+        return new JavaUrlRequest(callback, mExecutorService, executor, url, mUserAgent);

[pauljensen, 2015/12/14 20:02:05]

can we make this call createRequest(blah, blah, blah, blah,
REQUEST_PRIORITY_MEDIUM), or better yet, can you make give
CronetEngine.createRequest(without priority) an impl that does this?

[Charles, 2015/12/15 22:32:36]

Done.

+    }
+
+    @Override
+    public UrlRequest createRequest(
+            String url, UrlRequest.Callback callback, Executor executor, int priority) {
+        return new JavaUrlRequest(callback, mExecutorService, executor, url, mUserAgent);
+    }
+
+    @Override
+    BidirectionalStream createBidirectionalStream(String url, BidirectionalStream.Callback callback,
+            Executor executor, String httpMethod, List<Map.Entry<String, String>> requestHeaders) {
+        throw new UnsupportedOperationException(
+                "Can't create a bidi stream - httpurlconnection doesn't have those APIs");
+    }
+
+    @Override
+    boolean isEnabled() {
+        return true;
+    }
+
+    @Override
+    public String getVersionString() {
+        return "CronetHttpURLConnection/" + Version.getVersion();
+    }
+
+    @Override
+    public void shutdown() {
+        mExecutorService.shutdown();
+    }
+
+    @Override
+    public void startNetLogToFile(String fileName, boolean logAll) {}
+
+    @Override
+    public void stopNetLog() {}
+
+    @Override
+    public byte[] getGlobalMetricsDeltas() {
+        return new byte[0];
+    }
+
+    @Override
+    public void enableNetworkQualityEstimator(Executor executor) {}
+
+    @Override
+    void enableNetworkQualityEstimatorForTesting(
+            boolean useLocalHostRequests, boolean useSmallerResponses, Executor executor) {}
+
+    @Override
+    public void addRttListener(NetworkQualityRttListener listener) {}
+
+    @Override
+    public void removeRttListener(NetworkQualityRttListener listener) {}
+
+    @Override
+    public void addThroughputListener(NetworkQualityThroughputListener listener) {}
+
+    @Override
+    public void removeThroughputListener(NetworkQualityThroughputListener listener) {}
+
+    @Override
+    public URLConnection openConnection(URL url) throws IOException {
+        return url.openConnection();
+    }
+
+    @Override
+    public URLConnection openConnection(URL url, Proxy proxy) throws IOException {
+        return url.openConnection(proxy);
+    }
+
+    @Override
+    public URLStreamHandlerFactory createURLStreamHandlerFactory() {
+        // Returning null causes this factory to pass though, which ends up using the platform's
+        // implementation.

[pauljensen, 2015/12/14 20:02:05]

Hmm this isn't documented anywhere that I can find, but it does appear to be how
Android's implementation works.

[Charles, 2015/12/15 22:32:36]

Acknowledged.

+        return new URLStreamHandlerFactory() {
+            @Override
+            public URLStreamHandler createURLStreamHandler(String protocol) {
+                return null;
+            }
+        };
+    }
+}