refactor browser download utility

editor/scriptProperties.ts

@@ -282,12 +282,7 @@ module TDev
 
                 ScriptProperties.firstTime = false
 
-                var link = <HTMLAnchorElement>window.document.createElement('a');
-                link.href = res.dataurl;
-                (<any>link).download = "microbit-" + Script.getName().replace(/[^\w]+/g, " ").trim().replace(/ /g, "-") + ".hex"
-                var click = document.createEvent("Event");
-                click.initEvent("click", true, true);
-                link.dispatchEvent(click);
+                HTML.browserDownload(res.dataurl, "microbit-" + Script.getName().replace(/[^\w]+/g, " ").trim().replace(/ /g, "-") + ".hex"); 
             })
             .done(() => {},
             e => {

lib/Picture.ts

@@ -681,12 +681,7 @@ module TDev.RT {
                 }
                 else {
                     var url = this.canvas.toDataURL('image/png');
-                    var link = <HTMLAnchorElement>window.document.createElement('a');
-                    link.href = url;
-                    (<any>link).download = defaultName;
-                    var click = document.createEvent("Event");
-                    click.initEvent("click", true, true);
-                    link.dispatchEvent(click);
+                    HTML.browserDownload(url, defaultName);
                 }
                 return defaultName;
             });

rt/html.ts

@@ -896,6 +896,15 @@ module TDev.HTML {
         r.setChildren(elts)
         return r;
     }
+    
+    export function browserDownload(href: string, filename: string) {
+        var link = <HTMLAnchorElement>window.document.createElement('a');
+        link.href = href;
+        (<any>link).download = filename
+        var click = document.createEvent("Event");
+        click.initEvent("click", true, true);
+        link.dispatchEvent(click);
+    }
 
     export function showNotification(msg: HTMLElement) {
         elt("root").appendChild(msg);