Fix using Cesium inside of Electron apps.

Our Node.js detection was imperfect and unnecessary, we should have been
checking for the existence of `XMLHttpRequest` instead.

Fixes #6671

Author: mramato

Source/Core/FeatureDetection.js

@@ -163,14 +163,6 @@ define([
         return isFirefox() && firefoxVersionResult;
     }
 
-    var isNodeJsResult;
-    function isNodeJs() {
-        if (!defined(isNodeJsResult)) {
-            isNodeJsResult = typeof process === 'object' && Object.prototype.toString.call(process) === '[object process]'; // eslint-disable-line
-        }
-        return isNodeJsResult;
-    }
-
     var hasPointerEvents;
     function supportsPointerEvents() {
         if (!defined(hasPointerEvents)) {
@@ -238,7 +230,6 @@ define([
         isFirefox : isFirefox,
         firefoxVersion : firefoxVersion,
         isWindows : isWindows,
-        isNodeJs: isNodeJs,
         hardwareConcurrency : defaultValue(theNavigator.hardwareConcurrency, 3),
         supportsPointerEvents : supportsPointerEvents,
         supportsImageRenderingPixelated: supportsImageRenderingPixelated,

Source/Core/Resource.js

@@ -1834,14 +1834,15 @@ define([
             }).end();
     }
 
+    var noXMLHttpRequest = typeof XMLHttpRequest === 'undefined';
     Resource._Implementations.loadWithXhr = function(url, responseType, method, data, headers, deferred, overrideMimeType) {
         var dataUriRegexResult = dataUriRegex.exec(url);
         if (dataUriRegexResult !== null) {
             deferred.resolve(decodeDataUri(dataUriRegexResult, responseType));
             return;
         }
 
-        if (FeatureDetection.isNodeJs()) {
+        if (noXMLHttpRequest) {
             loadWithHttpRequest(url, responseType, method, data, headers, deferred, overrideMimeType);
             return;
         }

Specs/Core/FeatureDetectionSpec.js

@@ -115,8 +115,4 @@ defineSuite([
             expect(FeatureDetection.imageRenderingValue()).not.toBeDefined();
         }
     });
-
-    it('detects Node.js', function() {
-        expect(FeatureDetection.isNodeJs()).toBe(false);
-    });
 });