Fix throttling in scroll view

Summary:
Setting minimal throttle to 1/60 causes dropped updates.

Let's take following example

Each frame is 16.666 MS.

Frame1: [________didScroll is called towards end of the frame_]

Frame2: [_didScroll is called towards beginning of the frame_________]

update from Frame 2 doesn't propagate because we set throttle to 16MS thinking that `onScroll` is called for each frame.

If Javascript specified value below 1/60 it is basically asking for every update.

Reviewed By: shergin, mdvacca

Differential Revision: D17829926

fbshipit-source-id: e7b07fd09581cd5053aa27a62cf6f6ddb2193783

React/Fabric/Mounting/ComponentViews/ScrollView/RCTScrollViewComponentView.mm

@@ -119,10 +119,15 @@ - (void)updateProps:(Props::Shared const &)props oldProps:(Props::Shared const &
     // Zero means "send value only once per significant logical event".
     // Prop value is in milliseconds.
     // iOS implementation uses `NSTimeInterval` (in seconds).
-    // 16 ms is the minimum allowed value.
-    _scrollEventThrottle = newScrollViewProps.scrollEventThrottle <= 0
-        ? INFINITY
-        : std::max(newScrollViewProps.scrollEventThrottle / 1000.0, 1.0 / 60.0);
+    CGFloat throttleInSeconds = newScrollViewProps.scrollEventThrottle / 1000.0;
+    CGFloat msPerFrame = 1.0 / 60.0;
+    if (throttleInSeconds < 0) {
+      _scrollEventThrottle = INFINITY;
+    } else if (throttleInSeconds <= msPerFrame) {
+      _scrollEventThrottle = 0;
+    } else {
+      _scrollEventThrottle = throttleInSeconds;
+    }
   }
 
   MAP_SCROLL_VIEW_PROP(zoomScale);