Allow customized refreshControl in ScrollView for Android

Summary:
Original Android's refreshControl in ScrollView is tightly coupled with AndroidSwipeRefreshLayout. If someone use `ref=` for RefreshControl in ScrollView, it does nothing since RefreshControl in Android return null.

This change allows customized  RefreshControl especially for `ref=` as well as making ScrollView's code clearer.
Closes https://github.com/facebook/react-native/pull/5623

Reviewed By: svcscm

Differential Revision: D2890072

Pulled By: nicklockwood

fb-gh-sync-id: a8fc7746bcc050a6e46fedf3583979f4cb9021b6

Libraries/PullToRefresh/PullToRefreshViewAndroid.android.js

@@ -16,7 +16,6 @@ var RefreshLayoutConsts = require('UIManager').AndroidSwipeRefreshLayout.Constan
 var View = require('View');
 
 var onlyChild = require('onlyChild');
-var processColor = require('processColor');
 var requireNativeComponent = require('requireNativeComponent');
 
 var NATIVE_REF = 'native_swiperefreshlayout';
@@ -68,7 +67,7 @@ var PullToRefreshViewAndroid = React.createClass({
   render: function() {
     return (
       <NativePullToRefresh
-        colors={this.props.colors && this.props.colors.map(processColor)}
+        colors={this.props.colors}
         enabled={this.props.enabled}
         onRefresh={this._onRefresh}
         progressBackgroundColor={this.props.progressBackgroundColor}