Convert Inspector to call ref.measure

Summary:
`node` is passed to us from react devtools. We can call .measure on that directly instead of using findNodeHandle and UIManager. This makes this call compatible with Fabric.

Changelog:
[Internal]

Reviewed By: mdvacca

Differential Revision: D19152052

fbshipit-source-id: 05ab6d55f3a79221d99289f0341eb25352b96899

Libraries/Inspector/Inspector.js

@@ -18,7 +18,6 @@ const React = require('react');
 const ReactNative = require('../Renderer/shims/ReactNative');
 const StyleSheet = require('../StyleSheet/StyleSheet');
 const Touchable = require('../Components/Touchable/Touchable');
-const UIManager = require('../ReactNative/UIManager');
 const View = require('../Components/View/View');
 
 const invariant = require('invariant');
@@ -153,11 +152,7 @@ class Inspector extends React.Component<
   _onAgentShowNativeHighlight = node => {
     clearTimeout(this._hideTimeoutID);
 
-    if (typeof node !== 'number') {
-      node = ReactNative.findNodeHandle(node);
-    }
-
-    UIManager.measure(node, (x, y, width, height, left, top) => {
+    node.measure((x, y, width, height, left, top) => {
       this.setState({
         hierarchy: [],
         inspected: {