Prefer performance.now() over Date.now()

performance.now() is faster than Date.now() as there's no need to
consult the system clock. The more important part of this is that
performance.now() is monotonic and is guaranteed to never to backwards.

src/browser/TimeBasedDebouncer.ts

@@ -45,7 +45,7 @@ export class TimeBasedDebouncer implements IRenderDebouncer {
 
     // Only refresh if the time since last refresh is above a threshold, otherwise wait for
     // enough time to pass before refreshing again.
-    const refreshRequestTime: number = Date.now();
+    const refreshRequestTime: number = performance.now();
     if (refreshRequestTime - this._lastRefreshMs >= this._debounceThresholdMS) {
       // Enough time has lapsed since the last refresh; refresh immediately
       this._lastRefreshMs = refreshRequestTime;
@@ -57,7 +57,7 @@ export class TimeBasedDebouncer implements IRenderDebouncer {
       this._additionalRefreshRequested = true;
 
       this._refreshTimeoutID = window.setTimeout(() => {
-        this._lastRefreshMs = Date.now();
+        this._lastRefreshMs = performance.now();
         this._innerRefresh();
         this._additionalRefreshRequested = false;
         this._refreshTimeoutID = undefined; // No longer need to clear the timeout