Add an implementation of url_loader.mojom using OkHttp

This CL is the beginnings of an implementation of url_loader.mojom using the
OkHttp library. OkHttp is a relatively simple HTTP client library for Android
that implements HTTP/1.1 and HTTP/2.0. We might want to use OkHttp to bootstrap
into a more full-featured network_service implementation based on //net.

R=jamesr@chromium.org

Review URL: https://codereview.chromium.org/930673002

engine/src/flutter/shell/BUILD.gn

@@ -85,6 +85,7 @@ android_library("java") {
     "//mojo/public/java:bindings",
     "//mojo/public/java:system",
     "//mojo/services/network/public/interfaces:interfaces_java",
+    "//sky/services/oknet",
   ]
 }
 

engine/src/flutter/shell/apk/src/org/domokit/sky/shell/JavaServiceProvider.java

@@ -11,7 +11,9 @@ import org.chromium.mojo.system.MessagePipeHandle;
 import org.chromium.mojo.system.MojoException;
 import org.chromium.mojo.system.Pair;
 import org.chromium.mojo.system.impl.CoreImpl;
+import org.chromium.mojom.mojo.NetworkService;
 import org.chromium.mojom.mojo.ServiceProvider;
+import org.domokit.oknet.NetworkServiceImpl;
 
 /**
  * A class to intialize the network.
@@ -42,6 +44,10 @@ public class JavaServiceProvider implements ServiceProvider {
 
     @Override
     public void connectToService(String interfaceName, MessagePipeHandle pipe) {
+        if (interfaceName.equals(NetworkService.MANAGER.getName())) {
+            NetworkService.MANAGER.bind(new NetworkServiceImpl(mCore), pipe);
+            return;
+        }
         pipe.close();
     }
 }