[PerfGraph]: Fix track headers getting squished.

Track headers for Track Groups were getting squished with the headers for tracks below it.

This CL also updates the trace file to include a track group,
to validate the fix.

Bug: 443216198 (follow-up fix)
Change-Id: Iea38bde438831bac194ef870bc1cb785ced891fb
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/6969011
Commit-Queue: Finnur Thorarinsson <[email protected]>
Reviewed-by: Connor Clark <[email protected]>

Author: finnurbreki

front_end/panels/timeline/ExtensionTrackAppender.ts

@@ -43,7 +43,8 @@ export class ExtensionTrackAppender implements TrackAppender {
     if (totalEntryCount === 0) {
       return trackStartLevel;
     }
-    this.#appendTopLevelHeaderAtLevel(trackStartLevel, expanded);
+    const compact = !this.#extensionTopLevelTrack.isTrackGroup && totalEntryCount < 2;
+    this.#appendTopLevelHeaderAtLevel(trackStartLevel, compact, expanded);
     return this.#appendExtensionTrackData(trackStartLevel);
   }
 
@@ -53,9 +54,10 @@ export class ExtensionTrackAppender implements TrackAppender {
    * header corresponds to the track name, in the latter it corresponds
    * to the track group name.
    */
-  #appendTopLevelHeaderAtLevel(currentLevel: number, expanded?: boolean): void {
-    const style =
-        buildGroupStyle({shareHeaderLine: true, collapsible: PerfUI.FlameChart.GroupCollapsibleState.IF_MULTI_ROW});
+  #appendTopLevelHeaderAtLevel(currentLevel: number, compact: boolean, expanded?: boolean): void {
+    const style = compact ?
+        buildGroupStyle({shareHeaderLine: true, collapsible: PerfUI.FlameChart.GroupCollapsibleState.NEVER}) :
+        buildGroupStyle({shareHeaderLine: false, collapsible: PerfUI.FlameChart.GroupCollapsibleState.ALWAYS});
     const headerTitle = this.#extensionTopLevelTrack.name;
     const jsLogContext = this.#extensionTopLevelTrack.name === '🅰️ Angular' ? VisualLoggingTrackName.ANGULAR_TRACK :
                                                                              VisualLoggingTrackName.EXTENSION;