[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 mInitComplete 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()) {

[mmenke, 2015/01/08 19:06:16]

If we're on a random executor thread, what does Looper.myLooper do?

[mef, 2015/01/08 21:17:02]

Returns null if the calling thread is not associated with a Looper.

+                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;

[mmenke, 2015/01/08 19:06:16]

IS there a reason we have to set load and init complete to true here, and not in
ensureInitialized?  Seems weird that we can end up calling System.loadLibrary
arbitrarily many times at once, and run initOnMainThread each time, though it
will only do stuff once.

[mef, 2015/01/08 21:17:02]

In order to set sLoadAndInitComplete in ensureInitialized we have to wait for
initialization to complete on main thread, which seems even uglier.

[mmenke, 2015/01/12 15:28:26]

I don't follow.  We're not blocking anywhere until sLoadAndInitComplete is set
to true, we're just using it to avoid double-initialize.  For correctness, we're
relying on the main loop executing things in order instead, and context
initialization also jumping over to the main thread.

[mef, 2015/01/12 17:19:56]

Done.

+        }
+    }
+
+    // Native methods are implemented in cronet_loader.cc.
+    private static native long nativeCronetInitOnMainThread(Context context);
+}