networking: Fix requests failing when turning network off and on (facebook#19709).

This bug is probably actually a bug in OkHttp: square/okhttp#4079
Both issues linked above contain extensive details about the issue, its likely origins and
how to reproduce it. A short summary of the issue and the fix in this commit:

On Android, disconnecting from the network somehow corrupts the idle connections in okhttp
clients. New requests made over these clients fail. This commit works around that bug by
clearing the idle connection pool when Android disconnects from the network.

Author: roberthoenig

ReactAndroid/src/main/java/com/facebook/react/ReactActivity.java

@@ -10,13 +10,20 @@
 import javax.annotation.Nullable;
 
 import android.app.Activity;
+import android.content.BroadcastReceiver;
+import android.content.Context;
 import android.content.Intent;
+import android.content.IntentFilter;
+import android.net.ConnectivityManager;
+import android.net.NetworkInfo;
+import android.os.AsyncTask;
 import android.os.Bundle;
 import android.view.KeyEvent;
 
 import com.facebook.react.modules.core.DefaultHardwareBackBtnHandler;
 import com.facebook.react.modules.core.PermissionAwareActivity;
 import com.facebook.react.modules.core.PermissionListener;
+import com.facebook.react.modules.network.OkHttpClientProvider;
 
 /**
  * Base Activity for React Native applications.
@@ -46,10 +53,33 @@ protected ReactActivityDelegate createReactActivityDelegate() {
     return new ReactActivityDelegate(this, getMainComponentName());
   }
 
+  private class EvictIdleConnectionsTask extends AsyncTask {
+    @Override
+    protected Object doInBackground(Object[] objects) {
+      OkHttpClientProvider.getOkHttpClient().connectionPool().evictAll();
+      return null;
+    }
+  }
+
   @Override
   protected void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
     mDelegate.onCreate(savedInstanceState);
+    
+    BroadcastReceiver br = new BroadcastReceiver() {
+        @Override
+        public void onReceive(Context context, Intent intent) {
+            Bundle extras = intent.getExtras();
+            NetworkInfo info = extras.getParcelable("networkInfo");
+            NetworkInfo.State state = info.getState();
+            if (state == NetworkInfo.State.DISCONNECTED) {
+              new EvictIdleConnectionsTask().execute();
+            }
+        }
+    };
+    final IntentFilter intentFilter = new IntentFilter();
+    intentFilter.addAction(ConnectivityManager.CONNECTIVITY_ACTION);
+    getApplicationContext().registerReceiver(br, intentFilter);
   }
 
   @Override