[system analyzer] Dont try to render empty timeline tracks

Change-Id: Ibcfdfa7c6f8e5c13f6f2a5098fc7fde4fa15f3c4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3172757
Auto-Submit: Sathya Gunasekaran  <gsathya@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76962}

tools/system-analyzer/view/timeline/timeline-track-stacked-base.mjs

@@ -24,7 +24,7 @@ export class TimelineTrackStackedBase extends TimelineTrackBase {
   set data(timeline) {
     super.data = timeline;
     this._contentWidth = 0;
-    this._prepareDrawableItems();
+    if (timeline.values.length > 0) this._prepareDrawableItems();
   }
 
   _handleDoubleClick(event) {