Adding overwrite flag to has flags

src/base64.ts

@@ -1,8 +1,8 @@
 import global from '@dojo/shim/global';
 import has, { add as hasAdd } from '@dojo/has/has';
 
-hasAdd('btoa', 'btoa' in global);
-hasAdd('atob', 'atob' in global);
+hasAdd('btoa', 'btoa' in global, true);
+hasAdd('atob', 'atob' in global, true);
 
 /**
  * Take a string encoded in base64 and decode it

src/has.ts

@@ -4,13 +4,13 @@ import has, { add } from '@dojo/shim/support/has';
 export * from '@dojo/shim/support/has';
 export default has;
 
-add('object-assign', typeof global.Object.assign === 'function');
+add('object-assign', typeof global.Object.assign === 'function', true);
 
-add('arraybuffer', typeof global.ArrayBuffer !== 'undefined');
-add('formdata', typeof global.FormData !== 'undefined');
+add('arraybuffer', typeof global.ArrayBuffer !== 'undefined', true);
+add('formdata', typeof global.FormData !== 'undefined', true);
 add('filereader', typeof global.FileReader !== 'undefined', true);
-add('xhr', typeof global.XMLHttpRequest !== 'undefined');
-add('xhr2', has('xhr') && 'responseType' in global.XMLHttpRequest.prototype);
+add('xhr', typeof global.XMLHttpRequest !== 'undefined', true);
+add('xhr2', has('xhr') && 'responseType' in global.XMLHttpRequest.prototype, true);
 add('blob', function () {
 	if (!has('xhr2')) {
 		return false;
@@ -21,8 +21,8 @@ add('blob', function () {
 	request.responseType = 'blob';
 	request.abort();
 	return request.responseType === 'blob';
-});
+}, true);
 
-add('node-buffer', 'Buffer' in global && typeof global.Buffer === 'function');
+add('node-buffer', 'Buffer' in global && typeof global.Buffer === 'function', true);
 
-add('fetch', 'fetch' in global && typeof global.fetch === 'function');
+add('fetch', 'fetch' in global && typeof global.fetch === 'function', true);