Fixed black ARTSurfaceView

Summary:
If we draw using `drawRect:` with possible transparent pixels, we have to have `isOpaque = YES`.
https://developer.apple.com/documentation/uikit/uiview/1622622-isopaque

Differential Revision: D6609013

fbshipit-source-id: e483fd38b09c07e33b8b424d22c7a1adf81e6916

Libraries/ART/ARTSurfaceView.m

@@ -15,6 +15,15 @@
 
 @implementation ARTSurfaceView
 
+- (instancetype)initWithFrame:(CGRect)frame
+{
+  if (self = [super initWithFrame:frame]) {
+    self.opaque = NO;
+  }
+
+  return self;
+}
+
 - (void)insertReactSubview:(UIView *)subview atIndex:(NSInteger)atIndex
 {
   [super insertReactSubview:subview atIndex:atIndex];