fix($httpBackend): use ActiveX XHR when making PATCH requests on IE8

IE8's native XHR doesn't support PATCH requests, but the ActiveX one does.

I'm also removing the noxhr error doc because nobody will ever get that error.

Closes angular#2518
Closes angular#5043

Author: IgorMinar

docs/content/error/httpBackend/noxhr.ngdoc

@@ -1,12 +1,12 @@
 'use strict';
 
-var XHR = window.XMLHttpRequest || function() {
+function createXhr(method) {
+  // IE8 doesn't support PATCH method, but the ActiveX object does
   /* global ActiveXObject */
-  try { return new ActiveXObject("Msxml2.XMLHTTP.6.0"); } catch (e1) {}
-  try { return new ActiveXObject("Msxml2.XMLHTTP.3.0"); } catch (e2) {}
-  try { return new ActiveXObject("Msxml2.XMLHTTP"); } catch (e3) {}
-  throw minErr('$httpBackend')('noxhr', "This browser does not support XMLHttpRequest.");
-};
+  return (msie <= 8 && lowercase(method) === 'patch')
+      ? new ActiveXObject('Microsoft.XMLHTTP')
+      : new window.XMLHttpRequest();
+}
 
 
 /**
@@ -28,11 +28,11 @@ var XHR = window.XMLHttpRequest || function() {
  */
 function $HttpBackendProvider() {
   this.$get = ['$browser', '$window', '$document', function($browser, $window, $document) {
-    return createHttpBackend($browser, XHR, $browser.defer, $window.angular.callbacks, $document[0]);
+    return createHttpBackend($browser, createXhr, $browser.defer, $window.angular.callbacks, $document[0]);
   }];
 }
 
-function createHttpBackend($browser, XHR, $browserDefer, callbacks, rawDocument) {
+function createHttpBackend($browser, createXhr, $browserDefer, callbacks, rawDocument) {
   var ABORTED = -1;
 
   // TODO(vojta): fix the signature
@@ -57,7 +57,9 @@ function createHttpBackend($browser, XHR, $browserDefer, callbacks, rawDocument)
         delete callbacks[callbackId];
       });
     } else {
-      var xhr = new XHR();
+
+      var xhr = createXhr(method);
+
       xhr.open(method, url, true);
       forEach(headers, function(value, key) {
         if (isDefined(value)) {

src/ng/httpBackend.js

@@ -1572,6 +1572,10 @@ function MockHttpExpectation(method, url, data, headers) {
   };
 }
 
+function createMockXhr() {
+  return new MockXhr();
+}
+
 function MockXhr() {
 
   // hack for testing $http, $httpBackend

src/ngMock/angular-mocks.js

@@ -53,7 +53,7 @@ describe('$httpBackend', function() {
         })
       }
     };
-    $backend = createHttpBackend($browser, MockXhr, fakeTimeout, callbacks, fakeDocument);
+    $backend = createHttpBackend($browser, createMockXhr, fakeTimeout, callbacks, fakeDocument);
     callback = jasmine.createSpy('done');
   }));
 
@@ -250,7 +250,7 @@ describe('$httpBackend', function() {
       expect(response).toBe('response');
     });
 
-    $backend = createHttpBackend($browser, SyncXhr);
+    $backend = createHttpBackend($browser, function() { return new SyncXhr() });
     $backend('GET', '/url', null, callback);
     expect(callback).toHaveBeenCalledOnce();
   });
@@ -426,7 +426,7 @@ describe('$httpBackend', function() {
 
 
     it('should convert 0 to 200 if content', function() {
-      $backend = createHttpBackend($browser, MockXhr);
+      $backend = createHttpBackend($browser, createMockXhr);
 
       $backend('GET', 'file:///whatever/index.html', null, callback);
       respond(0, 'SOME CONTENT');
@@ -437,7 +437,7 @@ describe('$httpBackend', function() {
 
 
     it('should convert 0 to 404 if no content', function() {
-      $backend = createHttpBackend($browser, MockXhr);
+      $backend = createHttpBackend($browser, createMockXhr);
 
       $backend('GET', 'file:///whatever/index.html', null, callback);
       respond(0, '');
@@ -465,7 +465,7 @@ describe('$httpBackend', function() {
 
       try {
 
-        $backend = createHttpBackend($browser, MockXhr);
+        $backend = createHttpBackend($browser, createMockXhr);
 
         $backend('GET', '/whatever/index.html', null, callback);
         respond(0, '');
@@ -480,7 +480,7 @@ describe('$httpBackend', function() {
 
 
     it('should return original backend status code if different from 0', function () {
-      $backend = createHttpBackend($browser, MockXhr);
+      $backend = createHttpBackend($browser, createMockXhr);
 
       // request to http://
       $backend('POST', 'http://rest_api/create_whatever', null, callback);