use performance.mark to get entry to timeline (#101271)

src/vs/code/electron-browser/workbench/workbench.js

@@ -55,6 +55,7 @@ bootstrapWindow.load([
 ],
 	function (workbench, configuration) {
 		perf.mark('didLoadWorkbenchMain');
+		performance.mark('workbench-start');
 
 		return process['lazyEnv'].then(function () {
 			perf.mark('main/startup');

src/vs/workbench/browser/workbench.ts

@@ -414,6 +414,10 @@ export class Workbench extends Layout {
 
 			// Telemetry: startup metrics
 			mark('didStartWorkbench');
+
+			// Perf reporting (devtools)
+			performance.mark('workbench-end');
+			performance.measure('perf: workbench create & restore', 'workbench-start', 'workbench-end');
 		}
 	}
 }