[Cronet] Hook up library loader, system proxy and network change notifier to async api.

components/cronet/android/java/src/org/chromium/net/CronetLibraryLoader.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.Handler;
+import android.os.Looper;
+
+import org.chromium.base.JNINamespace;
+
+/**
+ * CronetLibraryLoader loads and initializes native library on main thread.
+ */
+@JNINamespace("cronet")
+public class CronetLibraryLoader {
+    /**
+     * Synchronize access to sLoadAndInitComplete and initialization routine.
+     */
+    private static final Object sLoadAndInitLock = new Object();
+    private static boolean sLoadAndInitComplete = false;
+
+    /**
+     * Ensure that native library is loaded and initialized. Can be called from
+     * any thread, the load and initialization is performed on main thread.
+     */
+    public static void ensureInitialized(
+            final Context context, final UrlRequestContextConfig config) {
+        synchronized (sLoadAndInitLock) {
+            if (sLoadAndInitComplete) {
+                return;
+            }
+            System.loadLibrary(config.libraryName());
+            // Init native Chromium URLRequestContext on Main UI thread.
+            Runnable task = new Runnable() {
+                public void run() {
+                    initOnMainThread(context);
+                }
+            };
+            // Run task immediately or post it to the UI thread.
+            if (Looper.getMainLooper() == Looper.myLooper()) {
+                task.run();
+            } else {
+                new Handler(Looper.getMainLooper()).post(task);
+            }
+        }
+    }
+
+    private static void initOnMainThread(final Context context) {
+        synchronized (sLoadAndInitLock) {
+            if (sLoadAndInitComplete) {
+                return;
+            }
+            NetworkChangeNotifier.init(context);
+            // Registers to always receive network notifications. Note
+            // that this call is fine for Cronet because Cronet
+            // embedders do not have API access to create network change
+            // observers. Existing observers in the net stack do not
+            // perform expensive work.
+            NetworkChangeNotifier.registerToReceiveNotificationsAlways();
+            nativeCronetInitOnMainThread(context);
+            sLoadAndInitComplete = true;
+        }
+    }
+
+    // Native methods are implemented in cronet_loader.cc.
+    private static native long nativeCronetInitOnMainThread(Context context);
+}