RefreshControl Position Bug

Summary:
Refresh bug facebook#7976
This bug has persisted for 3 versions of React Native.   Currently everyone is having to do a silly fix, documented in the bug.   I spent an hour trying to find the source of the bug.   Failing to find the issue quickly, I've just decided to make this simple bugfix.

According to janicduplessis facebook#7976 we will likely be re-writing this control in iOS 10.
Closes facebook#9249

Differential Revision: D3817227

fbshipit-source-id: f98282aadeca3e85239836f589eda901d454f2ce

Author: GantMan

React/Views/RCTRefreshControl.m

@@ -33,6 +33,12 @@ - (void)layoutSubviews
 {
   [super layoutSubviews];
 
+  // Fix for bug #7976
+  // TODO: Remove when updating to use iOS 10 refreshControl UIScrollView prop.
+  if (self.backgroundColor == nil) {
+    self.backgroundColor = [UIColor clearColor];
+  }
+
   // If the control is refreshing when mounted we need to call
   // beginRefreshing in layoutSubview or it doesn't work.
   if (_currentRefreshingState && _isInitialRender && _initialRefreshingState) {