Fix measureInWindow for view-backed Nodes

Summary:
This patch fixes measureInWindow for Nodes backed by Views.
Whereas the intention was to call the super implementation when we have a
Node backed by a View, we instead called the super implementation of
measure, which doesn't measure relative to window.

Differential Revision: D3607890

ReactAndroid/src/main/java/com/facebook/react/flat/FlatUIImplementation.java

@@ -195,7 +195,11 @@ public class FlatUIImplementation extends UIImplementation {
     FlatShadowNode node = (FlatShadowNode) resolveShadowNode(reactTag);
     if (node.mountsToView()) {
       mStateBuilder.ensureBackingViewIsCreated(node);
+      if (relativeToWindow) {
+        super.measureInWindow(reactTag, callback);
+      } else {
         super.measure(reactTag, callback);
+      }
       return;
     }