[tools][system-analyzer] Fix Chunk Selection and Consecutive file upload

Bug fixes:

* Wrong time range selection of timeline chunks handled by mouse events.
* Consecutive file uploads does not create a new Model object causing
bugs on timeline-track start and end times.

Bug: v8:10644

Change-Id: I3d31ddda1ffca70c18c87dd103f2b788713c2911
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2379863Reviewed-by: Sathya Gunasekaran  <gsathya@chromium.org>
Commit-Queue: Zeynep Cankara <zcankara@google.com>
Cr-Commit-Position: refs/heads/master@{#69598}

tools/system-analyzer/index.mjs

@@ -106,8 +106,13 @@ class App {
     console.log("source positions: ", sourcePositions);
   }
   handleFileUpload(e) {
+    this.restartApp();
     $("#container").className = "initial";
   }
+  restartApp() {
+    this.#state = new State();
+    this.#navigation = new Navigation(this.#state, this.#view);
+  }
   // Map event log processing
   handleLoadTextMapProcessor(text) {
     let mapProcessor = new MapProcessor();

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

@@ -157,7 +157,9 @@ defineCustomElement('./timeline/timeline-track', (templateText) =>
 
     positionToTime(posX) {
       let rect = this.timeline.getBoundingClientRect();
-      let posClickedX = posX - rect.left + this.timeline.scrollLeft;
+      let timeStartOffset = this.data.startTime * this.#timeToPixel;
+      let posClickedX =
+        posX - rect.left + this.timeline.scrollLeft + timeStartOffset;
       let selectedTime = posClickedX / this.#timeToPixel;
       return selectedTime;
     }