Merge from vscode 313ede61cbad8f9dc748907b3384e059ddddb79a (#7436)

* Merge from vscode 313ede61cbad8f9dc748907b3384e059ddddb79a

* fix strict null checks

src/vs/base/test/common/markdownString.test.ts

@@ -0,0 +1,19 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the Source EULA. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import * as assert from 'assert';
+import { MarkdownString } from 'vs/base/common/htmlContent';
+
+suite('markdownString', () => {
+
+	test('escape', () => {
+
+		const mds = new MarkdownString();
+
+		mds.appendText('# foo\n*bar*');
+
+		assert.equal(mds.value, '\\# foo\n\n\\*bar\\*');
+	});
+});