[tools][system-analyzer] Fix timeline scaling

- Make sure the viewport size of the svg is adjusted properly when
  scaling
- Fix an off-by-one when calculating Chunk groups

Bug: v8:10644
Change-Id: I56e857a8aa1a67e408bcfb08ed126e6bfdb0ce1b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3641177
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Patrick Thier <pthier@chromium.org>
Commit-Queue: Patrick Thier <pthier@chromium.org>
Auto-Submit: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80473}

tools/system-analyzer/helper.mjs

@@ -3,11 +3,11 @@
 // found in the LICENSE file.
 
 export class Group {
-  constructor(key, id, parentTotal, entries) {
+  constructor(key, id, parentTotal, entries, length = 0) {
     this.key = key;
     this.id = id;
     this.entries = entries;
-    this.length = entries.length;
+    this.length = length || entries.length;
     this.parentTotal = parentTotal;
   }
 
@@ -41,7 +41,7 @@ export function groupBy(array, keyFunction, collect = false) {
       continue;
     }
     let entries = collect ? [each] : sharedEmptyArray;
-    group = new Group(key, id++, array.length, entries);
+    group = new Group(key, id++, array.length, entries, 1);
     groups.push(group);
     keyToGroup.set(key, group);
   }

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

@@ -244,6 +244,7 @@ export class TimelineTrackBase extends V8CustomElement {
     this.hitPanelNode.style.width = `${width}px`;
 
     const ratio = this._scaleContent(width) || 1;
+    this.timelineChunks.style.width = `${width / Math.min(1, ratio)}px`;
     this._drawMarkers();
     this._selectionHandler.update();