Fix 'Undefined' in Timestamp column for media

The timestamps have been being rendered as 'Undefined' for a while now.
Apparently there was a drive-by change to this string that just broke
things and there wasn't a test to catch it.

Bug: none
Change-Id: I725c06b3ebc1d1fd85d03cd24071b419c431861f
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/7804752
Auto-Submit: Ted (Chromium) Meyer <tmathmeyer@chromium.org>
Reviewed-by: Mathias Bynens <mathias@chromium.org>
Commit-Queue: Jack Franklin <jacktfranklin@chromium.org>
Reviewed-by: Jack Franklin <jacktfranklin@chromium.org>

Author: tmathmeyer

front_end/panels/media/EventDisplayTable.test.ts

@@ -0,0 +1,66 @@
+// Copyright 2026 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import {assert} from 'chai';
+
+import {describeWithEnvironment} from '../../testing/EnvironmentHelpers.js';
+
+import * as Media from './media.js';
+
+describeWithEnvironment('EventDisplayTable', () => {
+  it('correctly displays the timestamp for events', () => {
+    const eventDisplayTable = new Media.PlayerEventsView.PlayerEventsView();
+    const event1 = {
+      timestamp: 1000,
+      value: JSON.stringify({event: 'testEvent', data: 'data1'}),
+    } as Media.MediaModel.PlayerEvent;
+
+    eventDisplayTable.onEvent(event1);
+
+    const rootNode = (eventDisplayTable as unknown & {
+                       dataGrid: {
+                         rootNode: () => {
+                           children: Media.PlayerEventsView.EventNode[],
+                         },
+                       },
+                     }).dataGrid.rootNode();
+    assert.lengthOf(rootNode.children, 1);
+
+    const firstNode = rootNode.children[0] as Media.PlayerEventsView.EventNode;
+
+    // Verify the data property is set correctly
+    assert.strictEqual(firstNode.data['displayTimestamp'], '0.000');
+
+    // Verify the cell is created with the correct content for the 'displayTimestamp' column
+    const cell = firstNode.createCell('displayTimestamp');
+    assert.strictEqual(cell.textContent, '0.000');
+  });
+
+  it('subtracts the first event time from subsequent events', () => {
+    const eventDisplayTable = new Media.PlayerEventsView.PlayerEventsView();
+    const event1 = {
+      timestamp: 1000,
+      value: JSON.stringify({event: 'testEvent', data: 'data1'}),
+    } as Media.MediaModel.PlayerEvent;
+
+    const event2 = {
+      timestamp: 1234.5678,
+      value: JSON.stringify({event: 'testEvent2', data: 'data2'}),
+    } as Media.MediaModel.PlayerEvent;
+
+    eventDisplayTable.onEvent(event1);
+    eventDisplayTable.onEvent(event2);
+
+    const rootNode = (eventDisplayTable as unknown & {
+                       dataGrid: {
+                         rootNode: () => {
+                           children: Media.PlayerEventsView.EventNode[],
+                         },
+                       },
+                     }).dataGrid.rootNode();
+    const secondNode = rootNode.children[1] as Media.PlayerEventsView.EventNode;
+
+    assert.strictEqual(secondNode.data['displayTimestamp'], '234.568');
+  });
+});

front_end/panels/media/EventDisplayTable.ts

@@ -42,7 +42,7 @@ export interface EventDisplayColumnConfig {
 }
 
 export const enum MediaEventColumnKeys {
-  TIMESTAMP = 'display-timestamp',
+  TIMESTAMP = 'displayTimestamp',
   EVENT = 'event',
   VALUE = 'value',
 }