Enable click and open mailto links in Markdown preview (#36795)

src/vs/base/common/network.ts

@@ -38,5 +38,7 @@ export namespace Schemas {
 
 	export const file: string = 'file';
 
+	export const mailto: string = 'mailto';
+
 	export const untitled: string = 'untitled';
 }

src/vs/platform/opener/browser/openerService.ts

@@ -40,10 +40,10 @@ export class OpenerService implements IOpenerService {
 
 		const { scheme, path, query, fragment } = resource;
 		let promise: TPromise<any>;
-		if (scheme === Schemas.http || scheme === Schemas.https) {
-			// open http
-			dom.windowOpenNoOpener(resource.toString(true));
 
+		if (scheme === Schemas.http || scheme === Schemas.https || scheme === Schemas.mailto) {
+			// open http or default mail application
+			dom.windowOpenNoOpener(resource.toString(true));
 		} else if (scheme === 'command' && CommandsRegistry.getCommand(path)) {
 			// execute as command
 			let args: any = [];