Fix the potential bug for network inspector when receiving xhr objects without an "_index" property

Summary: It sometimes happens that there are already some existing `XMLHttpRequest` objects before we turn on the network inspector. So it is a must to check whether a `XMLHttpRequest` object has a property `_index` to determine if it should be tracked.

Reviewed By: davidaurelio

Differential Revision: D3635184

fbshipit-source-id: a5552d7244c994b0fe782ac35baae39ec7488494

Author: Siqi Liu

Libraries/Inspector/NetworkOverlay.js

@@ -109,6 +109,9 @@ class NetworkOverlay extends React.Component {
     }.bind(this));
 
     XHRInterceptor.setRequestHeaderCallback(function(header, value, xhr) {
+      if (xhr._index === undefined) {
+        return;
+      }
       const networkInfo = this._requests[xhr._index];
       if (!networkInfo.requestHeaders) {
         networkInfo.requestHeaders = {};
@@ -118,12 +121,18 @@ class NetworkOverlay extends React.Component {
     }.bind(this));
 
     XHRInterceptor.setSendCallback(function(data, xhr) {
+      if (xhr._index === undefined) {
+        return;
+      }
       this._requests[xhr._index].dataSent = data;
       this._genDetailViewItem(xhr._index);
     }.bind(this));
 
     XHRInterceptor.setHeaderReceivedCallback(
       function(type, size, responseHeaders, xhr) {
+        if (xhr._index === undefined) {
+          return;
+        }
         const networkInfo = this._requests[xhr._index];
         networkInfo.responseContentType = type;
         networkInfo.responseSize = size;
@@ -141,6 +150,9 @@ class NetworkOverlay extends React.Component {
         responseType,
         xhr,
       ) {
+        if (xhr._index === undefined) {
+          return;
+        }
         const networkInfo = this._requests[xhr._index];
         networkInfo.status = status;
         networkInfo.timeout = timeout;

Libraries/Utilities/XHRInterceptor.js

@@ -82,7 +82,7 @@ const XHRInterceptor = {
     };
 
     // Override `setRequestHeader` method for all XHR requests to intercept
-    // the request headers, then pass them through the `openCallback`.
+    // the request headers, then pass them through the `requestHeaderCallback`.
     XMLHttpRequest.prototype.setRequestHeader = function(header, value) {
       requestHeaderCallback(header, value, this);
       originalXHRSetRequestHeader.apply(this, arguments);