Implement XHR timeout for Android and IOS natively.

Summary:
Opening this in a separate PR but the discussion can be viewed on #4832.

Basically, this is a native implementation and is a bit more elegant. The consensus on my previous PR was that it should be done natively rather than in JS.

There's now no maximum valid timeout value and a timeout of 0 will never time out.

ontimeout isn't implemented (yet) in this PR.

cc nicklockwood ide philikon
Closes https://github.com/facebook/react-native/pull/5038

Reviewed By: svcscm

Differential Revision: D2838743

Pulled By: nicklockwood

fb-gh-sync-id: 774f864ac35082bf522f7665f4311bd3affbe82c

ReactAndroid/src/main/java/com/facebook/react/modules/network/NetworkingModule.java

@@ -15,6 +15,8 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.io.Reader;
 
+import java.util.concurrent.TimeUnit;
+
 import com.facebook.react.bridge.Arguments;
 import com.facebook.react.bridge.GuardedAsyncTask;
 import com.facebook.react.bridge.ReactApplicationContext;
@@ -113,19 +115,25 @@ public final class NetworkingModule extends ReactContextBaseJavaModule {
   }
 
   @ReactMethod
+  /**
+  * @param timeout value of 0 results in no timeout
+  */
   public void sendRequest(
       String method,
       String url,
       final int requestId,
       ReadableArray headers,
       ReadableMap data,
-      final boolean useIncrementalUpdates) {
+      final boolean useIncrementalUpdates,
+      int timeout) {
     Request.Builder requestBuilder = new Request.Builder().url(url);
 
     if (requestId != 0) {
       requestBuilder.tag(requestId);
     }
 
+    mClient.setConnectTimeout(timeout, TimeUnit.MILLISECONDS);
+
     Headers requestHeaders = extractHeaders(headers, data);
     if (requestHeaders == null) {
       onRequestError(requestId, "Unrecognized headers format");