DevTools: [Documentation] Disable external XHR requests in documentation tests

LayoutTests/inspector/documentation/documentation-test.js

Index: LayoutTests/inspector/documentation/documentation-test.js
diff --git a/LayoutTests/inspector/documentation/documentation-test.js b/LayoutTests/inspector/documentation/documentation-test.js
new file mode 100644
index 0000000000000000000000000000000000000000..73dd5eede5f0138af8b2a306cc2bcd0326e4eca8
--- /dev/null
+++ b/LayoutTests/inspector/documentation/documentation-test.js
@@ -0,0 +1,23 @@
+function initialize_DocumentationTests()
+{
+
+InspectorTest.mockLoadXHR = function(urlPrefix, responseText)
+{
+    var originalLoadXHR = window.loadXHR;
+    window.loadXHR = function(url)
+    {
+
+        if (url.startsWith(urlPrefix))
+            return new Promise(load);
+
+        return originalLoadXHR(url);
+
+        function load(successCallback)
+        {
+            successCallback(responseText);
+            return;
+        }
+    }
+}
+
+}